Comparisons

Black Mesa is a remade version of Half-Life with several overhauls to the remake. Half-Life being a 21-year-old game seemed outdated today because of its graphics and designs, and now the community called Crowbar Collective remade the whole Half-Life game. During the production, the game was ended with a 7-year cliffhanger waiting for Xen to be released. 7 years later, near the end of 2019, Xen was released, from start to finish.

General

 * Black Mesa doesn't have a training course, though some of the developers said it was cut for obvious reasons.
 * Half-Life is made from a modified Quake engine called GoldSrc, whilst Black Mesa is made with the Source Engine
 * A Half-Life walkthrough is estimated to be finished in 3 hours, whilst Black Mesa is estimated to be finished in around 6-8 hours.
 * The G-Man appears more often in Black Mesa.
 * The vending machines give 15 cans of soda, while in the original, it only gave 10 cans soda. When hitting the vending machine, you can grab them, while in the original, you cannot grab the sodas.
 * The screen will flash green once something teleported.
 * All weapons will have inspecting animation when acquired for the first time.
 * When the player dies, the NPC will react to Gordon's death similar to Half-Life 2.
 * When the player dies, it will be a realistic firstperson-view death instead of instantly lying down.

Walkthrough
Black Mesa Inbound Anomalous Materials Unforeseen Consequences Office Complex "We've Got Hostiles!" Blast Pit Power Up On A Rail Apprehension Residue Processing Questionable Ethics Surface Tension "Forget About Freeman" Lambda Core Xen Gonarch's Lair Interloper Nihilanth End Game
 * Half-Life's tram ride is estimated to be around 5 minutes, whilst Black Mesa's is estimated to be around 7 minutes, this gives the player a chance to look around inside the Black Mesa Research Facility.
 * Later in Anomalous Materials, one of the scientists would say "Wasn't the tram ride a little longer, today?"
 * Barney can be seen at the entrance of his checkpoint.
 * Some of the people will greet you or glance at you going to work.
 * A guard before you enter the lab would say "Aw man, you cut the ponytail! Sell out."
 * When throwing things or props to scientists and guards (only in this chapter), they will reply to you with the expression of being angry or annoyed.
 * When seeing the G-Man and a scientist arguing, the G-Man will look to Gordon, thus the scientist will blind the windows.
 * In the cafeteria, instead of one scientist observing everything in the vending machine, a guard will replace his spot, minus the observing part.
 * In the cafeteria, when you explode the microwave, instead of a scientist getting shocked from it, a guard will approach the microwave and say "Cus uh, that was you-know-who's lunch" retconning Dr. Magnusson from Half-Life 2: Episode Two.
 * After exploding the microwave, the guard will mock you with his innumerable list of dirty and clean puns.
 * In the locker area, when acquiring the H.E.V, Gordon will do an inspecting animation and the scientist nearby you will admire how you look with the H.E.V.
 * In Half-Life 1, you can acquire 15 armor, whilst in Black Mesa, you can acquire 30 armor via charging station and battery found in your locker.
 * In the locker area, there will be a scientist asking help for a toilet paper, if you want to give him the toilet paper, you can. It can be found near the shelves of the sink.
 * In the elevator, the option to go down via ladder is now locked until Unforeseen Consequences.
 * The time, 8:50 AM, is displayed on the monitor on the ceiling. It will change to 9:01 AM once reaching the test chamber. Later, in Unforeseen Consequences, when going back to the observation room, the monitor is not displaying the time anymore, instead, the time can be seen in one of the panels, at that time it was already 9:47 AM.
 * Isaac Kleiner and Eli Vance now have their respective models.
 * Inside the test chamber, there is a monitor that shows what's going on in the observation room.
 * The monitor will turn into static once the Anti-Mass Spectrometer starts to malfunction.
 * When the sample is delivered, the cart will not move by side-to-side, instead, it's mechanism is changed to move only forward and backward.
 * When the sample is inserted, the sample cannot be pulled back.
 * When during the harmonic reflux Gordon is experiencing, you will be teleported in one of the Xen caverns from Gonarch's Lair instead of an open Xen area, and during the Vortigaunts scene, you cannot move and the Vortigaunts will try to get you back to Earth.
 * The player will be damaged by 30 health (armor will not be affected) during the intro of the chapter. Your health will always be 70 after waking up, damaging yourself before the accident will add up back to 70 HP.
 * The player wakes up instead of standing around in the test chamber.
 * The guard cannot be revived after going out of the test chamber.
 * Isaac Kleiner will admire the Headcrab in the jar.
 * A survived scientist will scream for help during the continuous blasts.
 * A guard zombie can be seen burning after leaving the observation room.
 * A torso scientist zombie can be also seen burning and crawling to you when entering the laser room.
 * The Crowbar is moved to the office areas.
 * The guard you reunite will be invincible, instead of being vulnerable from the original.
 * Originally in the 2012 version, he would die by one of the Zombies by either clawing him to death or strangling him to death.
 * In Half-Life, flares were usable weapons but cut, in Black Mesa, they can be used to burn Zombies and Headcrabs.
 * In Half-Life, when going back to the locker room, the "magically" and "mysteriously" battery can return in your locker to gain 30 armor, but in Black Mesa, when going back to the locker room, you cannot get armor from the suit charger whether you acquired it or you missed it, however, the battery will stay if you didn't acquire it earlier.
 * Back in the entrance, instead of a scientist falling to his death, a guard replaces his spot.
 * The doors in the office areas will automatically open slowly and shut closely patterns.
 * The retinal scanner is removed, requiring to attach it back to open the doors.
 * There is a frozen office on the left when entering Sector B, and a combusted debris to the right, it ends with an elevator that leads to the resembling intro.
 * Instead of 2 Houndeyes going towards the scientist, a Headcrab Zombie replaces its' spot.
 * In Half-Life 1, it seems that the scientist on the vent is trying to get in but fails horribly and one scientist who was just standing there watching his friend die, in Black Mesa, the 2 scientists are cooperating to get there and they also failed miserably.
 * There is no point, but the vent that the scientist tried to enter can be accessible via stacking but leads to a dead end.
 * Before encountering the G-Man again, Barnacles will infest the ceilings.
 * Instead of the casual getting-in, this storage area changed the entrance on the maintenance area below it.
 * There is a task to enter the other side, which is raising the temperature of the freezer.
 * The sewers have locked gates to prevent the players from doing shortcuts and making players explore more.
 * In the sewers, there will be zombies, taking that lone Headcrab's spot.
 * In the elevator, you cannot get back up.
 * This part is somehow similar to Half-Life 2: Episode One, where the elevator can be seen in the explosives room.
 * The health station in the elevator section will be replaced into a security booth but with an H.E.V charger instead.
 * It is rather strange that the guards have an H.E.V charger instead of a First-Aid station since the guards don't have a suit that supports the H.E.V charger.
 * There is a throwback easter egg where you can repeatedly try to enter a non-accessible door, similar to inaccessible areas from Half-Life 1.
 * In Half-Life 1, the Houndeye is seen teleported above the crate, in Black Mesa, however, is moved to the Bullsquid's spot, thus the Houndeye releasing a sonic wave near an explosive crate and destroying the catwalk bridge.
 * In the transporting area, where you have to jump onto crates, the crates are physical and not stiff, making it a bit hard because of the prop itself stopping or denying your jump.
 * Before entering the elevator, there is a storage area also including explosives and 2 Houndeyes will teleport.
 * In one of the ventilation shafts, with a dead security guard, the fan is already disabled.
 * In the lounging area, the Barnacles will break the ceiling once you've stepped near their opening.
 * Strangely, in Half-Life: Source, the Barnacles will grab you up before the Barnacles' tongues position it to the ground.
 * In the storage area, the zombie will not break the door, instead, the player can open it and it appears that the zombie is devouring a scientist in the back.
 * In the lounge, there is a radio broadcasting an emergency broadcast involving the Resonance Cascade and guiding the citizens in New Mexico to be away from Black Mesa.
 * In the "help-my-buddy" scenario, after acquiring the shotgun, there will be 2 Vortigaunts spawning in on the way back.
 * In one of the offices, a Houndeye is seen watching television static, originally in Half-Life, the Houndeye's AI included admiring machines that are flashing or machines that emit light.
 * Before entering the turret room, there will be cover before you drop in.
 * The Headcrabs in the turret room will not stay in their position, they will tend to move forward to the open.
 * In the office area's security booth, there will be 2 scientists hiding, instead of a scientist turning off the lights and hiding.
 * In the office area, instead of the Vortigaunts staying in their position, they will teleport in surprise. Not all of them at once gets to be teleported, some of them will be teleported in front of you.
 * Before entering the office area's security booth, instead of Vortigaunts pinning down the scientist, 3 Headcrab Zombies take their spot.
 * The scientist who heard a transmission about the H.E.C.U will have his room.
 * When entering the shortcut path, it will not lead up to the turret controls instantly, in this scenario, an elevator is about to fall, and once you've reached the upper vent, the elevator falls.
 * In another storage area, the area itself is replaced as underpass access but without any supplies.
 * The vent has 2 routes, going to the left will end up to the underpass access, there will be supplies placed on the other vent, notice that the Headcrabs breaking out is removed. Going to the right ends up to the office with supplies, the slow-rotating fan is now replaced like an opposite, the fan will be stopping you and pushing you to the back, it can be disabled to go to the other side, notice that there no Headcrabs again at this point.
 * The cafeteria is overhauled. There are more Headcrab Zombies than Headcrabs.
 * The refrigerator is completely overhauled, the valve for transporting will be missing, and the transport is changed to manual from automatic.
 * The ventilation shaft after the refrigerator is optimized.
 * Instead of the scientist running down and opening the door, the scientist will be with the guard, but you can still open the door yourself, notice that the zombie is removed.
 * On the upper floor, it will have a terrace, similar to the one from The G-Man's encounter. Also, there will be 5 zombies. 2 Vortigaunts will spawn in after killing 4 of the zombies.
 * The zombie who will be breaking the wall open will be replaced with a door, thus removing the breaking animation.
 * When climbing the ladders, a clinging scientist will fall from the ledges, the way he dies is somehow 'magically' or 'stupid' because of the trigger activated when you're near him.
 * Originally in the 2012 version, he will die by falling, similar to Half-Life 1.
 * The elevator 'mysteriously' moves without anyone or anything pressing the button to go down.
 * In definite edition, the guard at the start fights a zombie but ends up dying
 * The first sentry's tripwire cannot be dodged nor avoided in any way.
 * The cafeteria is once again, overhauled. In the cafeteria, there will be 2 Vortigaunts who will be teleporting in different positions, one extra Vortigaunt will spawn once you've entered the cafeteria.
 * In the storage area with two sentry guns, there will be 2 Vortigaunts who will be teleporting in over the tripwire and before the tripwire.
 * On the other side of that storage area, there will be no crates to jump on.
 * When tripping the sentry's tripwire in the section of the wet floors, the scientists will find cover (if only you've set off the sentries or threw a grenade near them).
 * When hearing the announcement of "Attention! This announcement, this system is now under military command." There will be a transition between the regular announcement we heard as usual from Anomalous Materials and the deep-voiced we heard in this section.
 * However, the deep-voiced announcer can be heard before this chapter, it can be heard in the security booth from the elevator section of Unforeseen Consequences.
 * The catwalk section is half-broken.
 * The marines will not spawn in the 3rd storage area until you have reached that area.
 * More marines will spawn in the 2nd storage area when you have reached the upper floor.
 * The surface is slightly overhauled.
 * The ventilation shafts are now removed, thus making it straightforward and only heading to the main route.
 * Back in the security booth, you cannot press the button until the scientist has finished explaining about the grunts or killing him.
 * The intro with the Bullsquid is now replaced to be a transporting area, notice that the Headcrabs are again removed.
 * The zombie with the explosives cannot hurt the player even if near the wall.
 * There's another path instead of taking the elevator, which involves ladders.
 * There is a security booth with a radio, once again, it is messaging the citizens in New Mexico to stay away from Black Mesa, and if some of the citizens are showing any symptoms that are related to this disaster should be reported to a hospital immediately.
 * When the tram crashes, the player will not gain any air control, and the Bullsquids are removed at this point.
 * The Bullsquid in the radioactive pool is repositioned to the upper sections.
 * The massive radioactive pool now shows with actual radiation liquid than a solid green floor.
 * The catwalks cannot be broken via explosions.
 * The zombie originally seen on the Fuel Annex route is now repositioned to be resting.
 * The scientist who will die from blood loss will 'die dramatically' or fake his death instead of the usual popping death animation.
 * Originally in the 2012 version, he will die with the usual popping death animation.
 * The control room is overhauled.
 * The explosive crates add more explosives, such as the Satchel Charges.
 * Jenkins, the guard who will make bait for the Tentacles, is repositioned to where you met the dying scientist.
 * The Tentacles' pit will have a radioactive glow, and straight passage, instead of a curvy wormhole.
 * In the fuel annex route, there will be 2 drops when going down to the sewers, it doesn't matter which one do you need to pick. In the turbine section, the boards from the ceiling are removed and replaced with several vents to enter the fuel annex. The Oxygen and the Fuel buttons are replaced with valves to activate each of them, similar from the refrigerator from Office Complex, one of the valves is missing and is required to find them to activate.
 * In the power generator route, the Houndeyes will not charge at you, because their main script or trigger is to sleep. In the elevator, there will be a column guarding the ladder, and when using the elevator, it will also teleport a pack of Houndeyes, the elevator is repositioned to the ground. When entering the power generator, the rotating platforms are removed and instead, letting the player walk or run to the top. Smithers, the scientist who is cowardly hiding from the others, is now repositioned in one of the control rooms of the generator, the new way to activate the generators are going to the control rooms and pressing the buttons that are blinking green. Once going back, there will be 2 Houndeyes and a Vortigaunt teleporting in front of you.
 * There will be a monitor monitoring the Tentacles.
 * Once reaching down to the Tentacles' station, it is filled with disgusting materials, especially the skin texture from Xen and also the radioactive materials and plants that are currently growing and infesting.
 * Once reaching to the disconnected pipe section, the pipe that you'll place can be rather annoying because of the physical properties it has, it sometimes cannot be completely straight.
 * The Tripmines are displayed and can be acquired in a nearby crate instead of being stored in a crate.
 * There are more marines than the original, one of them uses the RPG to stagger the Gargantua.
 * When all of the marines are dead, the Gargantua will block your exit and making sure it burns you.
 * After finding cover, 2 Vortigaunts will teleport near the explosives instead of you luring them out.
 * The trigger when the Gargantua screams and destroys the catwalk is removed.
 * The section where 2 Vortigaunts spawn next to explosives that causes a chain reaction has more explosives than the original.
 * The room that shows a Bullsquid about to devour a marine with all of his weaponry now shows itself to attack the player instead of hiding in his hole.
 * The marine that is supposed to patrol the area of the 3 chambers changed, to let him get alerted is to destroy the sentry on the 3rd floor.
 * The option to go down to the generator room via elevator is disabled at first, instead, the player is intended to go down by stairs.
 * The Houndeyes will charge at you when you go down more.
 * All Leeches are removed.
 * The turbines don't function as a shortcut anymore.
 * After turning on the generator, more marines will return once you got back to the room with the explosives.
 * There will be a Marine Zombie in one of the marines' infirmary once returning.
 * When you're back in the track controls room, you have to open the gates to get to the power room.
 * In the power room, you'll have to plug in the plugs in their sockets so the transformers can be turned on.
 * In Half-Life 1, you'll get killed when passing by the transformers, but in Black Mesa, you can't. Notice the room for skipping through the transformer is removed.
 * There will be 2 trams available when arriving at the station, once again, it doesn't matter which one you will pick.
 * The guard will rotate the tracks for you instead of going back there yourself.
 * The barricade is replaced by a gate that will be later opened once you've turned the power back on.
 * The Barnacles after the guard reminding you to launch the rocket are removed before starting On A Rail.
 * On A Rail is completely optimized, thus making everything straightforward and all of the things from the original will be missing. Parts including the small ones that are changed in the On A Rail chapter are:
 * The sections to the rocket thrusters, and that other part that lead to a dead-end.
 * Unnecessary dead ends
 * Unnecessary wooden bridges
 * The suicidal marine section.
 * The Double Turrets will be replaced with M2 Browning Machine Guns manned by different marines.
 * 2nd (before the rocket) and 3rd (after the rocket) section only having 1 part.
 * The rails are not electrified.
 * There is a room of what used to be for the tram system on the left, inside it contains a Headcrab Zombie and a Headcrab.
 * The switchable rail directions are broken.
 * In the tram stop section, a plug that is required for the power in the control room is removed and dropped in the water, thus making the water electrified. The player should re-plug the plug to get the power back for the control room.
 * The Houndeyes from the main route will be moved, taking the Bullsquid's spot to the entrance to the control room.
 * The Bullsquid from the main route will be moved to the control room.
 * Inside the control room, instead of a sentry containing in it, A Bullsquid will take its spot. Once lowering the gate and opening the door, more enemies will teleport in such as a Vortiguant and Headcrabs.
 * In the tram elevator, instead of marines surrounding you, Sentry Guns will take their place. Upon reaching the top, there will be Sentry tripwires.
 * Originally in Half-Life, upon reaching the top, there should be a marine who will be able to launch a grenade from his MP5, however, in Black Mesa, a sentry will replace his spot, but without any explosives.
 * Originally in Half-Life, there should be Vortigaunts and Marines attacking each other in 2 different sections. However, in Black Mesa, this section removes the 1st section. The parts that are changed in Black Mesa:
 * The upper parts between the two sections are removed.
 * The 3 marines will be now 2 marines on the tram stop will be after the sentry who replaced the marine's spot and will charge at you.
 * The security booth is not fortified.
 * The batteries on the ceiling are removed.
 * More aliens will teleport once entering the entrance of the rocket.
 * The door will now be opened via lever instead of pushing yourself through
 * There is a new objective once reaching the rocket to get to the tram, which involves lowering the catwalk bridges to ascend.
 * There will 4 marines on the catwalks instead of 1.
 * Originally in Half-Life, there are 4 parts in the 3rd section, going through the grenadier trying to shoot you down, the transporting area, the neighboring railways that lead to 2 different locations, and the last double-barreled machine gun manned by a marine. However, in Black Mesa, 3 parts will be abridged into 1 part. The part that includes the following changes in Black Mesa:
 * After reaching the top, the first part will be another tram with marines, which resembles the part when you use the second tram for going to the suicidal marine part. The second part will be a grenadier shooting your tram down, but if you don't have the tram with you, the grenadier will try to shoot you down. The third part will be a complete resemblance to the last section of the original On A Rail chapter minus the Double Turret.
 * The rocket launching area is completely overhauled.
 * One obvious notice is that the pre-launching area and the launching area are abridged together.
 * The sniper is removed from the pre-launching area.
 * The control room displays a timer in one of the monitors for the launching time. Also, the announcer will countdown the timer.
 * In the freight transport, the lower level is larger.
 * When going to the room with the supplies of the crossbow darts and MP5 grenades, there is a water current that is going so fast that it pushes the player, the player can still move forward but slowly.
 * In the shark cage, the cage will fall after inspecting the crossbow or in a matter of seconds.
 * The door from the broken catwalk will be inaccessible as a shortcut.
 * After killing the first Ichthyosaur, proceeding to the next area will reward with more crossbow darts.
 * In the next flooded area, a Vortigaunt will teleport when the bridge is collapsed or reaching to the other side via an unintentional game guide.
 * In the area of the 3 giant pistons, the crate that was supposed to make a shortcut to the other side seems a bit hard, because it only gives you a small space to go up.
 * Once reaching to the other side, a Houndeye will replace the Bullsquid's spot for teleporting behind Gordon.
 * There will be an Apache in a launchpad which presumably will be used by the marines later on in Surface Tension.
 * The Assassin who will kill the guard who was going to warn Gordon will show up and kill him.
 * Even if the assassins didn't see you, their AI will automatically set into hunting mode. Once you've reached the storage area.
 * In the "storage room" it shows that the marines are hiding but after they turn off the lights, neither of them charges at Gordon.
 * The player will once again take damage by 55 health (armor will not be affected), presuming that Gordon was thrown to the ground. Once again, it will always stay in 45 HP, even if you took too much damage earlier.
 * Gordon wakes up formally in a trash compactor instead of a stack of crates suddenly or randomly breaking to wake him up.
 * The door to the control room will not be opened until the trash compactor is done compressing everything.
 * The marines who captured Gordon will be in the control room but ended up being dead because of a Marine Zombie.
 * A health kit will be placed in the control room to regain 25 health back with the Crowbar as well.
 * Instead of a vent as an exit, a chute will replace its spot to be more logical. The chute will be opened via lever from the control room.
 * A dead scientist can be seen with a lead pipe in his hand, this is a reference to Manhack Matt in Half-Life 2, in which Gordon has to help him fight off the first group of Manhacks.
 * Another health kit will be placed near the dead scientist near the water tank to regain 15 health back.
 * Instead of draining the water tank like an elevator to go down, the flow control is now inside the water tank and the elevator is removed. Also, a wheel is added to seal the pipe to be more logical.
 * When reaching the first part of the disposal facility, the guard will not shoot the Headcrabs for you, instead, he will be scared and get devoured by a Barnacle. Footsteps that shape like one of the guards' boots found near the radiation might be the reason why he was scared.
 * Instead of jumping through "skin" to get across, the fire is blocking Gordon's goal. The fire can be disabled via disabling the pressure in the propane room, the propane room also contains a burning Headcrab Zombie.
 * Despite the guard didn't drop his gun, a Glock-17 is found near the dead Guard Zombie.
 * After finishing the 2nd part of the disposal facility, there will be 2 pipes, going to the right will collapse the pipe and will combust instead of radiation droplets going from there. Also, a Guard Zombie can be seen underneath the left pipe.
 * In the 3rd part of the disposal facility, the radiation tank will be separated into 2.
 * After the wastewater part, all of the conveyor belts' directions are now broken and a grinder will replace all of the pistons' spots and can be disabled indefinitely. Under the conveyor belt and the machinery where Bullsquids originally fought is now larger.
 * The pistons that go horizontally from the second part are replaced with the usual pistons that go vertically.
 * Going through different areas through a different direction of the conveyor belts will require to crouch and jump repeatedly to get in and some of them are closed to prevent shortcuts.
 * The waste processing area adds a transporting area, to proceed to the next area since the previous area has certain restrictions.
 * In one of the waste processing areas, there will be a Tripmine as a weapon with batteries in the catwalks.
 * The Tripmines that are placed and set in the conveyor belts are removed.
 * After the waste processing area, where the organs and rotten meat are, will be larger.
 * Similar to Blast Pit, Houndeye's broken AI in this area is sleeping.
 * Instead of shooting one of the transformers' wires, a plank is making the lever stuck in the breaker.
 * An Alien Grunt without armor and a Hivehand is in a tube, presuming that scientists were testing on it. In the control room, 3 buttons indicate what should they do with it the red button burns it, the blue button shocks it, and the green button gasses it. Getting near it will not attack you nor will it be provoked, it will just bang its head to the glass.
 * Originally in the early Half-Life versions, it is possible that the Alien Grunt was supposed to be killed with something in its tube
 * There is a testing room that controls the Snark machine designed for target practicing in the target area.
 * The testing area with a container full of Headcrabs is removed, the testing area with 2 cages of Headcrabs from the 2nd floor will be taking its place since the 2nd floor doesn't exist in Questionable Ethics in Black Mesa. The 1st cage for the Headcrabs will be always open and the Bullsquid will take the Headcrabs' spot in the 2nd cage and will be always closed, it can be opened in the control room, the Snark that was originally in the 2nd cage is moved to a laboratory.
 * An office will be added for the guard to stay, once the player is near there, the guard will approach you and warn you what's up ahead.
 * If you brought the guard with you, the guard will sneak onto the crates and wait for your signal which is you shooting, even if you have something silent like the Crossbow, the guard will attack and they will also attack.
 * A testing area with aliens in tubes is added before proceeding to the Alien Grunts.
 * A Marine will be patrolling in the control room of the Alien Grunts in the tubes.
 * Setting off the Tripmines can let the Alien Grunts escape.
 * If you brought the guard with you, the guard will stay in the surgical room door.
 * The laboratory room is added which is considered miscellaneous, which also takes the spot of the Headcrabs in cages with 4 sensitive cages. Inside the laboratory, contains a Snark Nest, and the strangest thing contained there is a Xen-themed room filled with Headcrabs and 2 extra Snark Nests, there is a Cyanogen canister in the laboratory to gas out all of the Headcrabs.
 * In Lab D, there will be offices near the 'Tau Cannon wielders' and the pack of Houndeyes.
 * In the laser testing area, the cover can be removed by a plug to be more logical, instead of pushing a crate to get the cover back up.
 * After disabling the surgical machine, all of the scientists will proceed and if the guard was staying there, he would too.
 * Once getting back to the lobby, an ambush will occur.
 * After the ambush, 2 of the scientists will stay and if the guard was also there, he would stay too, and 1 scientist will 'help' you get to the Lambda Complex. He will die at the entrance of the lab.
 * There will be 3 extra marines waiting for you, instead of just 1.
 * The explosive entrance to Surface Tension is removed.
 * When reaching the guard booth, there will be 4 marines, 1 will be manning an M2 Browning Machine Gun and 3 of them will be waiting for the marine who's manning the M2 Browning Machine Gun's signal.
 * There will be gates to the dam, once reaching near there, the gates will close, forcing the player to use the truck to get across.
 * There will be 2 M2 Browning Machine Guns in the middle of the dam, they can be used to damage the Apache to save U-235 ammo.
 * There will be 2 Ichythosaurs in the reservoir, instead of one.
 * The water will be splashing to indicate if the sluice gate is opened.
 * In the desert area, the Apache will not fight back Gordon.
 * In the desert area, instead of the Tentacle returning as a side enemy being in the alternate area, a different area is remade. The whole area is designed like a shaft but later on, it seems to be used as a waste disposal area despite the chute being there similar to Residue Processing. The exit will also lead back to the marines' camp to prevent going in circles.
 * In the marines' camp, after opening the gate, more marines will come and get you.
 * In the minefield, the mines will be visible, but more mines are placed than the original and more Headcrabs are burrowed and will rise near the mines.
 * At the cliff, there are more marines than the original.
 * At the cliff, the bridge out of brittle planks cannot break anymore.
 * Once reaching in the catwalks, the Apache will make its last pass by.
 * In the booths at the cliff, there will be a supply cache of rockets. There is more supply cache of rockets in the garage.
 * At the end of the cliff, there will be boulders blocking your exit to prevent shortcuts and skipping. Once the Apache is down, the player can proceed.
 * In the first area of the Topside Motorpool, marines will drop flaming barrels of explosive barrels and the M1A1 Abrams will move in the middle of the road instead of staying near the garage.
 * In the second area of the Topside Motorpool, M2A3 Bradley will be replaced with a LAV-25
 * In the third area of the Topside Motorpool, no Alien Grunts will be dropped off by the Alien Aircraft, but just Vortigaunts. One of the Vortigaunts will set off the mines after dropping them off. When seeing the guard dying, a scientist will come and help him, but the Sniper from the vents scares him and runs away. The electrified radio tower can simply be disabled with the breaker on the side instead of blowing up the whole electric supply.
 * In the warehouse, there are 200% more explosions than the original and also more Headcrabs. The strange addition is that the leaking gas at the beginning doesn't combust.
 * In the fourth area of the Topside Motorpool, if you saved the guard, and acquiring the Hivehand to in front of him lets him say a 'unique' line. If you brought the guard with you, he will remind you that he and his buddy were finding a supplies lockup to fight off the marines. Inside the storage facility, there will be 5 marines, instead of 2. If you brought the guard with you the guard will be relieved seeing his buddy again, and take a break, but if you didn't the guard will trust that Gordon is not hostile. In the ruins, it will be completely ruined. In the launchpad, the garage door will only open once the V-22 Osprey is down. Atop the garage, will be another storage facility containing a BGM-71 TOW cannon replacing the M198 Howitzer to take M1A1 Abrams down.
 * In the fifth area of the Topside Motorpool, the area is highly overhauled. The Vortigaunts that will be teleported near the gate will be lesser than the original. After opening the gate, a battle will occur between the marines and Xenians. In the surprise ambush, the marines will not save you any room to stay in the vents, forcing the player to fight the grunts, as well as the bomb surprise, it will not allow you to get out of the garage, also forcing the player to go out through the blasted window via car. At the marine camp, an M2 Browning will replace the spot of the M198 Howitzer since there are already explosives attached to the gate. Originally in Half-Life, after the marine camp, it should be designed like a massive warehouse, but in Black Mesa, it is all replaced as it is redesigned as a launchpad, although all of the events are still the same as the original.
 * In the sixth and the last area of the Topside Motorpool, this area is once again, highly overhauled. While the battle is ongoing, an Alien Aircraft will be coming in and using its laser to destroy M1A1 Abrams, this script is, however, long, it will keep on going until the marines or the Xenians wins. Before heading inside the warehouse, there will be a new area that is almost infested with Snarks and Xen materials. Upon reaching the roof, there will be 2 snipers and 2 Marine Zombies stopping you from going inside the hatch or manhole. Inside the warehouse, the part that is full of Headcrabs is replaced with several Headcrab Zombies, also the next area will be blocked off with fire similar to Residue Processing, the same process as before too, lowering the pressure the fire to stop it. The next area is a hangar, which the player can choose either to go stealth to avoid fire from the marines, or loud to make things fast. Outside of the hangar, the guard will remind you where to go, the security booth, but there will be Xenians teleporting to stop you two from going to the security booth. Once getting inside the security booth, the guard will leave you to it. When reaching a police car's radio, the last emergency broadcast can be heard, saying that everyone must evacuate away from New Mexico.
 * In the Waste Processing Area 3, when the Gargantua is chasing you, there will be more vehicles than the original. The Gargantua's and radio tower's chance of going down is all in one blast. Upon reaching the Lambda Complex's doorstep, the gates cannot be destroyed but can be opened manually via the wheel on the left.
 * There will be 2 turrets instead of 1.
 * The turret will not attack you or the guard, it will only attack the Xenians.
 * The useless elevator path with a Snark mine is removed.
 * Snark mines will release more Snarks than the original.
 * In the steam pipes, the door locked with the padlock is now without a padlock.
 * Outside the base of the Lambda Complex, this area is overhauled. More marines exiting from the base to attack you. A camp nearby with supplies can help you keep up to the battle.
 * Inside the base of the Lambda Complex, a marine can be seen being swarmed with Snarks. A sentry before the elevator is changed to alarm controlled via tripwire, instead of automatic. Upon reaching the bottom of the base, there will be a pool of radiation instead of a leak-like design. M1A1 Abrams will not be used for fighting off the Xenians, instead, it will be operated. The battle between the marines and the Xenian will change into a garage instead of a warehouse-like design. The Xen Turret will be replaced with regular automated Sentries from the H.E.C.U.
 * The elevator has its controls to go down or up instead of itself moving down after turning its power
 * All of the assassins except 1 will hunt you and surround you when arriving at the storage area. There will be more assassins than the original.
 * At the transporting area, there will be more Xenians instead of just a group of Alien Grunts.
 * The elevator once again will have its controls to go down or up.
 * In the first area of the Lambda Complex, once arriving the first part before the coolant systems, a pack of Houndeyes will be charging at you. All of the Xenians that will be teleporting in after coming back to the main part of the area, are now changed to "going back after turning on the tanks and pumps" but with different spawn schedules. After going back from Coolant System 1, a pack of Houndeyes will charge at you, while going back from Coolant System 2, 2 Vortigaunts will shock you.
 * In both Coolant Systems, there will be more Vortigaunts teleporting in than the original, and more Vortigaunts who will be teleporting in after turning on the tanks and the pumps. It is required to open the drain cap to activate the pumps, instead of pulling a lever.
 * In Coolant System 1, the design will change and look like it was attempted by scientists. In the first part, a pack of Houndeyes will be charging at you.
 * In Coolant System 2, the design will change and look like it is heavily damaged. More Vortigaunts teleports in at this area.
 * In the access pipe, it will be always closed, once the tank and the pumps are activated, it will be opened with a button on its side.
 * In Level D of the Reactor Core, the lasers will not start until you turn on the power. The small lasers that will be rotating are removed. There will be scorch marks on which lasers will occur. Once reaching the top, the laser will melt through the door.
 * The broken elevator shaft will let you get across in 2 ways, safely go to the other side, or jump over like the original.
 * In Level B of the Reactor Core, teleporters will be emitting particles if choosing the right ones, on the top part of Level B, it will give you an elevator, which will take time to go down and up.
 * Port 1 will transform into a sort of a miscellaneous room instead of infinite dropping Headcrabs in brittle grates.
 * Port 5 will take you to 3 members stranded in the Lambda Complex, 2 scientists and 1 guard.
 * Port 6 will transform into a straight fall instead of fall damage with brittle grates breaking every time you drop.
 * In Level C of the Reactor Core, the radioactive pool will change into regular water, which if you fell, you will die via the moving platforms. However, you can still survive when the second platform that goes up and down goes down and reaching it.
 * The supply depot will be designed to look more advanced than the original. Before entering the supply depot, turrets will deploy which is still controlled by the Survey Team. Hunter will provide you with everything in your arsenal except the Hivehand and Snarks. Doctor Steinman will provide you the long-jump module and will open the gates for you.
 * In Level A of the Reactor Core, the holdout will provide you with supplies to take down the ambush.
 * The scientist who will be opening the portal cannot be killed.
 * There will be a transition of you teleporting to the border world, the Nihilanth sees you entering their world and Gordon seeing Nihilanth he is holding the portal, presuming that Nihilanth is keeping the portal open between Xen and Earth.
 * In Xen and Gonarch Lair's backgrounds, there will always be a giant structure similar to the Citadel in Half-Life 2, that stays there, because that's your primary objective to where to go.
 * All the parts of the Xen and so on are completely overhauled and added different goals to play through.
 * Supply caches will teleport on special occasions to let Gordon resupply and press on.
 * In all the parts of the Xen, several Protozoans are hovering around the Xen.
 * The border world has only 1 star.
 * Instead of landing in one of the cliffs like from the original, you will teleport in one of the caverns.
 * There is a laboratory of the Survey Team which looks like it is raided with Headcrabs. In the laboratory, a Cyanogen will be found in the table  which will be useful later on .
 * On the island, the objective will be extended into a 'Direct Intervention objective ' instead of releasing the butterflies/moths to activate the portal.
 * You will be teleported in a cavern again instead of a quick battle of the Gonarch.
 * Before battling the Gonarch, the chapter intends you to do a different objective which involves activating the power for the teleporter to Nihilanth's chamber.
 * The player is only allowed to fight the Gonarch in the cliff fight and the final standoff. Thus making the whole second section into just running away from her.
 * In one of the caverns, you will have a déjà vu about this cavern. It is the same cavern as you were experiencing harmonic reflux during the Resonance Cascade.
 * In the final standoff, you are going to fight the Gonarch above the web, instead of fighting her under the web. When damaging the Gonarch pretty well, the crystal from above will collapse and breaking the web.
 * There is an alternate way of killing the Gonarch, which is rather 'lazy' but quick. When bringing the Cyanogen from the laboratory from Xen, you can gas it and kill her.
 * This still triggers Nihilanth to say "Done, what have you done?"
 * Instead of teleporting to the next island, Gordon has to move on on-foot.
 * The first section from the original is removed, thus changing the first section to the second section of the original.
 * All Vortigaunts are friendly and are not hostile when you provoke them. Alien Controllers will control them to make them hostile to you.
 * The stations that will relieve you, will also relieve your armor.
 * There are several alarm systems, which a group of Alien Controllers will teleport in and control the situation.
 * In the first section called "Vortigaunt Camp" starts you off on the cliff with 2 Tentacles. In the next area, an Alien Grunt is seen beating the Vortigaunt to the ground, this part is similar after the Tentacle area minus the alarm system. In the next area, it will be a Vortigaunt village, which is not part of the original, but one of the events are part of the original are, the alarm system is moved here and activating the power to the teleporter will sound the alarm and Alien Controllers will teleport in to control the situation.
 * In the second section called "Gargantua's Lair" is rather short. In this area, you have to run away from several Gargantuas, this is somehow a modified event from the original second section to make things intense.
 * In the third section, it almost resembles the original third section. The only change is that one of the lifts can be overflowed and will sound the alarm and the Alien Grunt transport is removed.
 * In the fourth section, it almost resembles the original fourth section. The only change is the Alien Grunt factory and the Alien Grunt storage area aren't present.
 * In the fifth and ninth sections, in the last area only for the fourth section and all parts of the ninth section, resembles the last section minus the portal to the last island. Also, in the ninth section, the power sources to the force field are required to be disabled, and the player will be intended to disable those, there will be 3 rooms that will contain a power source for the force field, each power will be disabled in 1 room, each room will have Alien Controllers protected with crystals with different components in the room, this somehow almost resembles the last section.
 * The first room contains an Alien Controller protected with 3 crystals with several round-shaped boulders to throw at Gordon. Once reaching the power room, there are rotating lasers that can be avoided if the player times it carefully.
 * The second room contains a group of Alien Controllers but without any protection. Once reaching the power room, Gordon must avoid all the lasers when the shooting down the force field's power breaker, because the lasers will fall to the ground.
 * The third room contains an Alien Controller with 2 crystals several Vortigaunts to control them and be hostile to Gordon. Once reaching the power room, Gordon must avoid all the lasers while dropping to the ground and ascending to the top.
 * Alien Controllers will have crystals that they will use for armor.
 * In the sixth and eighth sections, again, it is rather short. It resembles an area from the original fourth section, the Alien Grunt storage area minus the tubes themselves. The Alien Grunts will teleport at that area to attack you instead of being 'hatched' from their tubes. Also, green crystals are placed to resupply your U-235 ammo.
 * In the tenth section, it resembles the last section. During the ascension, there will be 4 different waves.
 * The first wave will start you off being trapped and you will be in an open field with an Alien Controller protected with its crystal, they will use explosives to attack you.
 * The second wave will be hard, there will be 2 Alien Controllers with crystals still protecting them and several Alien Grunt tubes that the Alien Controllers will destroy and release the Alien Grunts.
 * The third wave will have 3 Alien Controllers with crystals still protecting them and the crystals will have more protection than the 2, 2 crystals will protect the Alien Controller at this point.
 * The fourth wave will descend the elevator by the Alien Controllers to try and finish off Gordon, this time they will not be protected, and if Gordon has killed enough, the elevator will start ascending once again.
 * Nihilanth's silhouette can be seen when you come in contact with his portal.
 * The screen will flash in red if you're near Nihilanth's portal.
 * Nihilanth's portal will have fires spreading.
 * Nihilanth's 3 different chambers are removed.
 * Supply caches are the only help to resupply and fight off the Nihilanth.
 * Nihilanth will have 3 crystals protecting them similar to the ones that the Alien Controllers use.
 * Nihilanth's healing crystals will be placed on the ground.
 * Nihilanth will have 3 stages when fighting.
 * In stage 1, Nihilanth will normally attack Gordon with mortars and electrical powers.
 * In stage 2, Nihilanth is beginning to be angry and starting to throw Gordon Earth's vehicles and materials and will start Earth bending.
 * In stage 3, Nihilanth is very angry and will stop using mortars, but use fire waves, more electrical powers, and shooting a giant laser at you frequently.
 * Nihilanth will stop attacking except his fire waves when Nihilanth's brain is exposed.
 * There are 3 different endings. The regular ending, the hat ending, and the pizza ending.
 * Instead of the Xen elevator descending from the original Half-Life, you will get a view of the giant structure exploding, but the time will stop and G-Man will start to talk to you.
 * This is a direct reference from Half-Life 2's ending.
 * The second location will not be Xen, but rather in the Crossfire deathmatch map with many casualties occurred.
 * The tram will rebuild itself before heading off in the fourth location, and the tram door will always be open if you want to accept the G-Man's deal and make it quick.
 * If Gordon denies the G-Man's offer, the tram will start corrupt and you will be teleported to an unknown part of Xen where many Xenians are fleeing Xen.

NPCs
Black Mesa Science Team Black Mesa Security Force Vortigaunt Headcrab Headcrab Zombie Barnacle Houndeye Bullsquid Black Mesa Ceiling Turret H.E.C.U Turret Hazardous Environment Combat Unit V-22 Osprey Tentacles Gargantua Ichthyosaur Black Ops Female Assassin Alien Grunt AH-64 Apache M1A1 Abrams LAV-25 Snark Alien Controller Xenian Turrets Gonarch Nihilanth
 * The scientists will have unique lines when interacting with them in specific times of events.
 * The female scientists are added into the game.
 * The female scientists will not wear a tie.
 * The scientists will react when you throw things at them.
 * In Anomalous Materials, before entering the test chamber, the scientist on the left is voiced by Kevan Brighting, the narrator of Stanley Parable.
 * In Unforeseen Consequences, the scientist who will open the door for the security office will stay there.
 * In Questionable Ethics, the 3 scientists will lead you back to the lobby. After the ambush, 1 of them will lead Gordon to the Lambda Complex but sadly dies at the entrance of the lab.
 * In Xen, there is a lab, made by the survey team. The lab is overrun when arriving there, in the whiteboards, one of them includes the discoveries of the life of Xen, another is a schedule of when will the next supply drop off, and lastly, the members who were with the survey team, 7 of them are marked "Missing" which they will be found later on.
 * In Gornarch's Lair, the 7 missing members of the survey team can be found in different areas, especially in caves.
 * At the beginning of Unforeseen Consequences, Isaac Kleiner will admire Lamarr in its jar. While Eli Vance will find someplace safe for Isaac so he could get his family.
 * The scientists' AI is similar to the Citizens in Half-Life 2 but without any weapon-purposed scripts.
 * The security guards have unique lines when interacting with them in specific times of events.
 * Strangely, they also have some of the Blue Shift lines, but unused.
 * The security guards will have 4 uniform variants, with helmet and vest, without a helmet but with a vest, without helmet and vest, with a helmet but without a vest.
 * The security guards can wield 3 different weapons, The Glock-17, the Colt Python, and the SPAS-12.
 * The security guards will start to irritate at you when you throw things at them.
 * Barney Calhoun will just be a minor character, he can be found at Black Mesa Inbound and can be heard later on in Gonarch's Lair in one of Dr. Horn's base as an easter egg.
 * The security guards can alert the player for nearby hazards such as grenades and NPCs.
 * The security guards can attack the Barnacle.
 * The security guards' AI is almost similar to the Civil Protection in Half-Life 2 but always set as friendly.
 * The Vortigaunt will dodge when the player aims at them.
 * The Vortigaunt will use a shockwave when the player is near them.
 * In the Earthbound chapters, they will be always hostile to the player. While in the Xen chapters, especially Interloper, they will be friendly. But they will be hostile, once the Alien Controllers control their minds to attack Gordon Freeman.
 * Even if provoking them or doing something wrong to them, they will still be friendly.
 * The Vortigaunt's AI is similar to Half-Life 2: Episode 2.
 * Since Black Mesa is made in Source Engine, there are similar things that the Headcrab can do in Half-Life 2 such as:
 * It can be killed/gibbed with heavy props.
 * Can jump off when stuck of cliffs or edges.
 * Can drown from water.
 * The Headcrab zombie will have 4 different variants such as the scientist zombie, the guard zombie, the marine zombie, and lastly, an H.E.V zombie which appears the host still has some armor left for the suit.
 * The Headcrab zombie will have torso-only variants similar to Half-Life 2.
 * The Headcrab zombie can be staggered when shot in specific parts of the host's body.
 * When shooting the Headcrab zombies in the chest to foot, the Headcrab can survive and leave the host.
 * The Headcrab zombie's AI is likely similar to Half-Life 2.
 * The Barnacle's health is increased thus making the Crowbar hit it 3 times instead of 1.
 * Since Black Mesa is made in Source Engine, there are similar things that the Headcrab can do in Half-Life 2 such as:
 * Grab up props.
 * Constricting the NPC when getting grabbed.
 * Slowly descends the tongue after consuming 1 NPC.
 * In the Xen chapters, the Barnacle also has its underwater counterpart, called Underwater Barnacle.
 * It will not ascend the tentacles up after consuming 1 NPC.
 * All of your weapons except the Crowbar, Glock-17, Crossbow, RPG, Hivehand, and explosives will be useless to kill this Barnacle.
 * There is an achievement that relates to a Barnacle devouring a Headcrab 10 times.
 * The Houndeye's back will glow bright blue when they are ready to release a sonic wave.
 * The Houndeye's sonic waves will not be visible on grounds, but rather on sight.
 * The Houndeye can die reaching on water.
 * In the Xen chapters, the Houndeye will have 2 different variants, such as the Suicidal Houndeye and the Knockback Houndeye.
 * The Suicidal Houndeye will charge at you to explode.
 * The Knockback Houndeyes will not inflict damage to you but knocks you off.
 * Regarding the "Black Mesa Decathalon Winner" achievement, the Knockback Houndeye's knockback sonic wave is considered as damage.
 * The Bullsquid is always calm when the player is out of sight of it.
 * The Bullsquid's acidic spit has more acidic spit than the original.
 * The acidic spit will trigger the H.E.V to say "Warning, hazardous chemicals detected"
 * If the acidic spit has reached to water, it will move slowly and stop eventually. Trying to touch a frozen/broken acidic spit will not inflict damage.
 * Bullsquids will not be hostile to one another.
 * Bullsquid's AI is somehow similar to the Antlion Workers in Half-Life 2: Episode Two, but modified.
 * The ceiling turrets are powered and can still be controlled by the Black Mesa.
 * The ceiling turret only has 1 variant, which is a combination of the 2 original ceiling turrets.
 * The ceiling turret's AI is almost similar to Half-Life 2: Episode One.
 * The H.E.C.U Turret can be retracted by interacting with them making it hostile to everything.
 * When retracted it can run out of bullets, but it can't if it still set to hostile to Gordon Freeman, the Science Team, the Black Mesa Security Force, and the Xenians.
 * The H.E.C.U Turret's tripwires will be gone when all of the turrets are terminated.
 * The H.E.C.U Turret's AI is almost similar to the Rewired Combine Turrets in Half-Life 2: Episode Two.
 * Though they still can be disabled even if they are fallen.
 * The grunts have unique idling lines, also including from Opposing Force.
 * Strangely they will say lines that they hit Gordon, even though he isn't hit by any of them.
 * The grunts have different variants, the beret, the gas mask, the helmet, the night vision goggles, the medic, the grenadier, and the sniper.
 * The beret can launch the grenade in the MP5's grenade launcher.
 * Strangely, when the beret drops, it acts as a small health kit, similar to the Combine Soldiers from Half-Life 2 when killing them at low health.
 * The gas mask deepens their voice just like the original but has no special benefits.
 * The helmet and the night vision variants are just regular grunts.
 * These variants seem to spawn in for special events, especially the night vision variants.
 * The Medics can heal their group.
 * When the Medic dies, it would drop a health kit.
 * The Medic's AI is similar to the Medic Rebel in Half-Life 2 but set as a hostile.
 * The Grenadiers can use the RPG for bigger threats including Gordon Freeman.
 * The Grenadier's AI is similar to the Rebel using the RPG in Half-Life 2 but set as a hostile.
 * The Grenadier has only 1 rocket to launch, so after launching, he will switch back to his MP5/Shotgun.
 * When the grenadier is still holding the RPG and then dies, the RPG doesn't drop.
 * The Sniper is almost identical to the original, but with a laser sight and real-time bullets for a change.
 * The Sniper's AI is likely similar to the Combine Sniper in Half-Life 2.
 * Marines dropping off is reduced to 2 instead of 4.
 * Will set on fire when heavily damaged instead of smoking in one of the rotors.
 * When destroyed, it's parts scatter around, instead of going off in a big blast.
 * It will emit an explosion to indicate if it is damaged.
 * The Osprey's AI is almost identical to the Combine Dropship in the Half-Life 2 series.
 * The damage for the impact is lowered.
 * The Gargantua cannot be killed, even with the Tau Cannon, Gluon Gun, nor any of the player's explosives.
 * The Gargantua's shockwave and punching mechanics are somehow removed.
 * The Ichthyosaur is faster.
 * The Female Assassin equips an Akimbo of Glock-17s.
 * The Glock-17s are not equipped with suppressors, but it uses the same sound as the Glock-17 but silenced.
 * The Female Assassin also has Long Fall Boots equipped to save them from falling similarly to Chell from the Portal series.
 * When the Female Assassin dies, it won't open up the night vision goggles.
 * The Female Assassin's ability to throw grenades is somehow removed.
 * The Female Assassin's AI is somehow similar to the cut enemy, Combine Assassin, from Half-Life 2 Beta.
 * The Alien Grunt shoots more hornets than the original.
 * However, the hornets aren't homing towards the player.
 * In the Earthbound chapters, their AI is to shoot hornets rapidly and charge, later in the Xen chapters, their AI appears to be more agile and they can jump onto platforms.
 * If the player and the Alien Grunt are a radius apart, the Alien Grunt will try to charge at Gordon. This changes the punching mechanic from the original.
 * The Alien Grunt has 4 variants, the armored with a Hivehand, the unarmored without a Hivehand, the recently-produced with armor and Hivehand, the recently-produced without armored and Hivehand.
 * The Armored with a Hivehand variant is the common Alien Grunt seen throughout Black Mesa and Xen.
 * The Unarmored without a Hivehand variant is the Alien Grunt that was released from its tube. The unarmored will likely just charge at you.
 * The recently-produced with Armor and Hivehand variant is the Alien Grunt seen in the alternate ending of Black Mesa. Their models are completely different including the one without armaments. The difference is their skin is paler, their backs appear to be burned out.
 * The recently-produced without Armor and Hivehand variant, however, is not seen anywhere throughout Xen.
 * The Alien Grunt's AI is somehow almost similar to the Hunter in Half-Life 2: Episode Two.
 * Will set on fire when heavily damaged instead of smoking in the rotor.
 * When destroyed, its parts will scatter around, instead of going off in a big blast.
 * It will emit an explosion to indicate if it is damaged.
 * The Apache has more health.
 * The Apache's AI is almost identical to the Hunter Chopper in the Half-Life 2 series but modified.
 * Will use both its machine gun and cannon.
 * Will set on fire when heavily damaged instead of not showing any clear big impacts.
 * When destroyed, its parts will scatter around, instead of exploding the turret.
 * M1A1 Abrams has more health.
 * M1A1 Abrams' AI is almost similar to the Combine APC in Half-Life 2 but modified a bit.
 * Replaces the M2A3 Bradley.
 * LAV-25 has no explosives to fire.
 * When destroyed, its parts will scatter around, instead of just exploding the turret.
 * Snarks are more agile, smaller, and will swarm when it comes to groups
 * Snarks can go loose when destroying the nest.
 * There are more Snarks in the Snark Mine.
 * Their appearance is changed, especially their glow.
 * Their secondary attack is changed to a cluster bomb type energy balls.
 * Can dodge when the player is aiming at it.
 * Can mind control Vortigaunts.
 * Can levitate objects, can be noticeable by emitting an orange glow.
 * Can teleport in when an alarm sounds to control the situation.
 * Original health is reduced.
 * Will start to spark if near to it.
 * More common around the Xen chapter.
 * Spawns more Bebcrabs than the original.
 * Her melee attacks deal great knockbacks.
 * Has a new attack for medium ranges, spreads 3 acids to attack the player.
 * Her mortar-like attack has changed, being recolored as green and will explode, can be shot to explode.
 * Later, this will turn into green acid as a final attack before she dies.
 * Has 2 layers to protect him, 3 crystals for the shield, 3 crystals for healing.
 * The healing crystals' health are reduced.
 * Can be blown off simultaneously via Satchel Charge.
 * Has a radioactive zone under it.
 * Teleport orbs are removed from his attacks, despite there being no chambers found outside the map.
 * Electrical orbs are now shot one at a time, instead of a spread
 * Has 4 new attacks, each getting worse by each phase.
 * Lasers
 * Phase 1 and 2, lasers are considered as supporting attacks, they will continuously keep on occurring.
 * Phase 3, the laser is still a supporting attack, but a targeting laser will mark where the laser will be shot, during at that part, Nihilanth will charge it and shield himself before Gordon gets to his back to attack.
 * Mortars
 * Phase 1 and 2, mortars are also considered as supporting attacks, they will continuously keep on occurring.
 * Shockwave
 * Phase 3, mortars are changed into a fiery shockwave and can deal great damage.
 * Throwing
 * Phase 2 and 3, he will spawn a vehicle and start throwing at you, this can be avoided by long jumping.
 * Rockbending
 * Phase 2 and 3, he will start to rise the rock formation from the ground, this tactic is to block Gordon's path.
 * There is a chance you can get stuck from this.
 * At Phase 3, when he is damaged enough, his brain will be exposed.

Weapons and Items
H.E.V. Mark IV Suit First Aid Station First Aid Kit H.E.V. Charging Station H.E.V. Battery Crowbar Glock-17 .357 Magnum/Colt Python H&K MP5 Franchi SPAS-12 Black Mesa Crossbow
 * Every weapon will have their inspecting animation when being acquired and just being idle.
 * The H.E.V. Suit has more details, seeing its system files, checking itself if the suit works properly when first equipping it.
 * The First Aid Station has more details, with tubes with some healing juice to see how much is left, led lights to indicate if it's almost drained out.
 * It will close when it's empty.
 * When reaching the max health, the sound will not continuously keep ongoing. The same also applies to the H.E.V. Charging Station.
 * There are 2 variants of the First Aid Kit.
 * The blue variant gives you +10 health. These are found commonly throughout Black Mesa. H.E.C.U. Medics can drop these if dead.
 * The green variant gives you +25 health. These are found rarely throughout Black Mesa. H.E.C.U. Medics may drop them at a lower chance.
 * The H.E.V. Charging Station has the same details with the First Aid Station but with 3 tubes of charging juice.
 * The battery itself can emit light, but it will be not enough.
 * The battery is smaller than Half-Life's battery.
 * From the free mod, the Crowbar's firing speed from hitting something was slowed down, similar to Half-Life 2's Crowbar's firing speed. Later in the Steam version, it is increased the same as Half-Life 1.
 * The Crowbar's first placement near the elevator shaft is relocated to one of the offices after escaping the main lobby of the Anomalous Materials Lab.
 * The Crowbar now has its own crosshair.
 * From the free mod, holding the primary and secondary button to shoot continuously wasn't implemented, similar to Half-Life 2's USP Tactical. Later in the Steam version, it can be shot continuously by holding the primary and secondary fire button.
 * The Glock's crosshair is wider than the original.
 * When doing the rapid-fire of the Glock-17, the crosshair will widen.
 * The entire magazine is reduced from 250 to 150. The same also applies to the MP5.
 * The full reload was not implemented in the free mod.
 * From the free mod, while reloading, Gordon can magically place the bullets in the slots without using the speed loader. Later in the Steam version, this is now fixed.
 * The .357 can now use its iron sights to aim.
 * The max bullets are reduced from 36 to 12 (free mod), then to 18.
 * The .357 shares the same crosshair as the Crowbar but smaller. The crosshair will hide when using the iron sights.
 * The clip is reduced from 50 to 30.
 * The max grenades are reduced from 10 to 3.
 * The full reload was not implemented in the free mod.
 * Black Mesa Security Guards can use MP5 but not used nor seen in the game.
 * The MP5 clip is replaced with the same clip from an MP5.
 * The max shells are reduced from 125 to 64.
 * Gordon will cock the shotgun when it's a full reload.
 * Black Mesa Security Guards can use SPAS-12, as seen in On A Rail and Lambda Core.
 * The SPAS-12's crosshair is wider.
 * From the free mod, the scope has the same functions from Half-Life 2's crossbow but using the scope, instead of zooming. Later in the Steam version, its scope was recreated to an awful function, with a poorly drawn crosshair on its end, stiff viewmodel, and lower mouse sensitivity.

RPG Tau Cannon Gluon Gun Hivehand Mk.2 Grenade Satchel Charge Snarks Flare Long Jump Module Supply Caches
 * From the free mod, the dart can ricochet. Later in the Steam version, it cannot anymore.
 * The darts are replaced with neurotoxin-treated darts.
 * The max darts are reduced from 50 to 10.
 * The crossbow's crosshair shares the same crosshair from Half-Life 1's Glock-17 crosshair.
 * By default, its' laser sight is always turned off. When finishing the inspecting animation from the first pickup, it will turn on.
 * Strangely, some are rather not supposed to happen when using the laser sight.
 * From the free mod, the rocket can somehow get stuck in some tight areas. The only way to fix this is to turn the laser sight off.
 * When not using the laser sight, and launching it, and enabling it during its flight, it might end up in a circular loop. Turn off the laser sight to fix this problem.
 * The RPG's crosshair is replaced with a wide separated cross. When the laser sight is active, the laser sight's crosshair will be rotating.
 * The Tau Cannon's emitted balls are removed, but only seen as an impact particle.
 * The Tau Cannon will emit a sound to indicate the charge shot is ready. It will also emit some sparks in the throttle to indicate it's overcharging rate.
 * The Tau Cannon cannot ricochet.
 * The Tau Cannon cannot penetrate through even charging it.
 * The Tau Cannon's crosshair is replaced with an octagon-shaped.
 * The Gluon Gun will leave marks when shot at the wall.
 * The Gluon Gun will disintegrate the killed target.
 * The Gluon Gun's beam is more blue-ish than cerulean color.
 * You can damage yourself with the Hivehand from being too close to the surface.
 * The hives will emit alien blood or honey when on the flight.
 * The hives will also spray alien blood when touching or impacting the surface.
 * The Hivehand's arm placement is shortened.
 * The grenade can be dropped, similar to Half-Life 2's grenades.
 * The grenade will emit smoking and sparking when it's ready to explode.
 * Grenades can be picked up and thrown away. Be careful!
 * Strangely, when pulling the pin out and switching to another weapon, it will not explode. It also applies during the state of throwing it and dropping it.
 * The satchel charge will fear the enemies and friendlies.
 * The satchel charge can still be picked up but not returnable after consuming it.
 * The satchel charge's controls are changed, the primary button for throwing it, secondary for detonating it.
 * Similar to the grenade it can be thrown away or dropped.
 * The Snark's explosion sound is lowered.
 * The Snark Nest can be destroyed thus releasing Snarks.
 * From Half-Life, the flare was an unused weapon used to burn enemies when the Post-Cascade is happening. It shares the same function as Black Mesa.
 * The flare can spread fire when there's an exposed gas leak.
 * Flares are commonly found in labs. In case of emergencies.
 * Flares are used to signal where the supply cache is nearby.
 * The Long Jump Module's controls are changed, instead of Duck Jumping, jumping twice will do its thing.
 * However, you cannot use them when your jump patterns are delayed.
 * The Long Jump Module has 3 bars, each of them indicates how many times you're able to use, so be careful of how many times you'll use them.
 * The Long Jump Module can save you from any fall during the Xen chapters.
 * The Long Jump Module is a great asset of dodging certain things, especially Gonarch.
 * These supplies will keep you going in the Xen chapters.
 * These caches will be glowing and emitting a sound, so keep an eye out on them.
 * These supply caches will be a useful asset for beating Nihilanth.