Black Mesa, an ambitious Fan Remake of Half-Life made with Valve's blessing, ramped up the difficulty of Half-Life, to the point you could go back to the original game and feel their hardest levels are easy in comparison. Likewise, the NPCs gained a brain and can now assist you properly in battle, provided you take care of them as much, too. Take a look!
- From a story perspective, the Xen aliens in general pose a much clearer threat to the military than in the original. While both versions have the military ultimately back off from the facility due to being overrun, it's shown far more often in Black Mesa—areas that once had few aliens now have more, and there are many set pieces that show soldiers being completely overwhelmed by aliens.
- Xen Aircrafts in the original never demonstrated the ability to attack ground targets, being exclusively an air-to-air combat aircraft. Here? Not only they can engage HECU fighter jets in a dogfight, but they are now capable of attacking ground based targets as seen in "Surface Tension" where they vaporize an MBT (alongside any unlucky HECU marines in the line of fire) and later in "Forget About Freeman" where they raze the remaining HECU forces escaping the facility.
- Houndeyes. They didn't pose much of a threat in the original game, but if you're not careful here, they'll mess you up. They move faster, no longer jump back when damaged, and their shockwaves do more damage, charge up in less than a second, and blur your screen a little while a ringing noise fills your ears. This goes double for their variants in Xen. The little fireball ones will explode if you so much as sneeze on them, and the knockback ones are huge and will send you flying. The first thing you see the latter one do, even, is throw down with a bullsquid.
- Vortigaunts/Alien Slaves. It was all too easy to completely avoid their attacks in in Half-Life, but here, they fight almost exactly like their stronger Half-Life 2 iterations, which makes them far more deadly. They can take more hits, and had their attack speed increased significantly. They also gain the shockwave attack from Episode Two, allowing them to push you away if you are close to them, and new to this game is their ability to weave to evade your attacks. Just like in Half-Life, they ambush you frequently by teleporting in, which is effective due to their fast attack time and accuracy. You'll be facing large groups of them at a time, especially in "Lambda Core".
- Bullsquids, despite their larger size, are now much quieter, and typically the last thing you'll hear before one comes out of cover and starts attacking you is the sound of it inhaling to fire a glob of toxic bile. You won't hear their iconic screaming in this game. They also spit a shower of acidic puke each time, instead of easily avoided projectiles like in the original Half-Life. Their hitpoints on Easy and Normal have also been buffed from the classic 40 to 80.
- The Gargantuas weren't immune to explosive weapons in the first game, but the mod now grants them invincibility to all attacks outside of scripted events. You won't be able to just kill these beasts with a massive stockpile of ammo, but rather, you have to use the environmental hazards present to kill them when they show up, and pray you can outrun them long enough to get to said hazards. What's more, one segment of "Interloper" drops you right into a Gargantua nest, and a Chase Scene ensues where you have to outrun dozens of them. On finally making a long jump across a pit they cannot cross, you're in the clear, and you look back to see all of them on the cliffs you've just left, roaring and flaming the air.
- The entire Hazardous Environment Combat Unit as a whole. They were already a dangerous threat in the original game, with their Cavalry Betrayal in "We've Got Hostiles" marking an increase in difficulty, but here, they go from Goddamned Bats to possibly the very epitome of Demonic Spiders. To wit:
- The grunts weren't pushovers in the original game, but now they do more damage, are much more accurate, and can take more punishment before going down. They aren't afraid to outright bum-rush you while soaking up your return fire. The 1.0 release gave them a considerable boost in intelligence; they now flank you, throw grenades more often to flush you out of cover, and even use suppressing fire on your last known position. Furthermore, they now have Combat Medics in the form of the Navy Hospital Corpsmennote , who are no longer relegated to the Glock. They wield MP5s - and occasionally shotguns - with the same deadly accuracy as their comrades. Lastly, there are now considerably more HECU marines who pack shotguns, and a few of them even have RPG launchers!
- Apaches have adopted many traits of the Combine Hunter-Chopper, including increased durability and immunity to small-arms fireExplanation . Originally, their low health meant they could be destroyed with a single rocket. Here, they can take up to at least a dozen rockets before going down note On top of that, their attack pattern has been revamped; while both their chain gun and missile attacks are telegraphed by distinctive noises (with the former only being fired in Hunter-Chopper-style bursts as opposed to full-auto whenever the player was in the Apache's line-of-sight), sufficiently damaging an Apache will cause it to release a full-on missile barrage, once again mirroring the Hunter-Chopper and its mine spam.
- The tanks in "Surface Tension" are nastier mainly because they can actually move, whereas in the original game they were basically glorified turrets (but still pretty dangerous.)
- The Black Ops Assassins are much, much more agile and accurate than their Half-Life iterations, and now wield two silenced pistols instead of having only one. They can't throw grenades anymore, but suffice to say they don't need to.
- Security Guards will occasionally be armed with SPAS-12s and Colt Pythons as opposed to exclusively using Glock-17s, and can also fire while moving in a similar fashion to the revamped HECU. They're also now smart enough to back away from melee enemies like zombies. Python-packing guards can hold their own against almost anything short of an Alien Grunt, and are among the deadliest NPCs in the whole game.
- While Alien Grunts initially appear to be a case of Adaptational Wimp, the ones fought on Xen are far more dangerous than in the original game, as not only are they significantly faster than they were in the original, they can now hop between platforms and will fire off their hivehands like crazy.
- Alien Controllers were never a pushover to start with; they were highly mobile, attacked in numbers and had powerful attacks, thus earning many players' hatred in the original game. The devs of Black Mesa took this a bunch of steps further: not only are they much more numerous and their attacks even stronger, but they can force the otherwise-peaceful Vortigaunts to attack and they have the ability to throw physics objects at the player, including explosives. In later stages, they even get smaller versions of their master's invulnerable Deflector Shields. This, combined with the much more evident cruelty they display towards their Vortigaunt slaves, makes them veritable Hate Sinks.
- The Gonarch was a fairly underwhelming encounter in the original game, which just ran around the arena, occasionally spawning baby headcrabs and spitting bile at you and occasionally hitting you if you got too close before running off, forcing you to chase it to do it again (two times); the entire fight would on average take about 5-6 minutes or so. The encounter with the Black Mesa version is an entire level, with the creature upgraded to a savagely aggressive Lightning Bruiser that can send you flying into oblivion with its charge attacks, crush you to a pulp by hurling huge chunks of rock at you, or spit blobs of explosive green plasma, and it hunts you through the vast caves of its lair in a running battle that lasts 20-30 minutes until you finally throw down with it in its nest. Its roars are also far more intimidating than the comical elephant-like trumpeting of the original version.
- The Nihilanth was akin to a Puzzle Boss in the original game, relying upon teleporting the player away from him and getting progressively weaker as the fight went on, with the puzzle needed to actually render him vulnerable being extremely simple. Here, he's lost most of the Puzzle Boss aspects but has become far more aggressive, teleporting in cars and chunks of Black Mesa to attack the player with, shooting death rays, raining explosive projectiles from above, and even causing gigantic rock formations to emerge from the ground to box the player in. And while he loses some of these as the fight progresses, the remaining attacks happen with increased frequency, making each one come off as a Desperation Attack.
- While on Xen, crates full of supplies will occasionally teleport near the player's location, with some of those drops serving as legitimate life-savers. The implication is that the science crew back in the Lambda Complex are tracking Freeman and sending help where they can, as opposed to just disappearing from the story.
