One thing is for certain about video games: there will always be more things to fight/shoot at/jump on/run from. One of the integral pieces of a video game is the challenge to overcome something, and most of the time that something is going to be an enemy out to get you. It doesn't matter what kind of enemy it is. It could be an armless Goomba from the Mario series or an Android assailant from Viewtiful Joe. All it matters is that its something that's only real goal is to keep you from progressing onward.
Some of these enemies are really memorable. Whether they were a low level mook (cannon fodder) or a high level boss near the end of the game, some enemies work their way into your psych, eating away at you and affixing themselves in your mind forever, often to the point where something that sounds like one of them can send chills down your spine. Here are X of them.
The Chainsaw Zombie: Resident Evil 4
When you first see it however, it's the opening moments of the game, and you have nothing but a pistol, a few grenades, and a shotgun. You're low on ammo, and yet this guy comes at you with everything he has. It doesn't matter what you send at him: bullets, grenades, eggs. He just keeps coming, and once he gets within swinging range you're pretty much doomed to see a Game Over screen. It's almost impossible to actually kill him the first time through, you have to run, and keep running, until the opening sequence is over. You can't hide...he'll find you....every time.
The next time you run into one, you're holding a vastly superior arsenal to the first time, and it makes...no difference whatsoever outside of the fact that you may have enough ammo to kill him this time around. If you're lucky enough to do so however, be prepared to skimp on bullets for the next few scenes. Later in the game, when you finally are packing the firepower to take one out with reasonable patience, the game just ups the ante. Why not two Chainsaw Zombies? Even more memorable is the absolutely terrifying mine cart ride where about halfway through, a Chainsaw Zombie drops into the cart right behind you. And they're never alone. There is always a small mob of Ganados traveling with them vying to kill you, so your attention is pretty divided.
The Chainsaw Zombie made my pulse rise every time I heard a chainsaw for years afterwards, and I'd grown up hearing them. To this day I still have memories of disbelief as I poured bullet after bullet into one, only to be rewarded with complete indifference. Run mortal. Run in fear. Image source: Resident Evil Wiki
The Splicers: Bioshock 1 and 2
The whole point of Bioshock's little world was one where people could do anything as long as it was for them. No one owed anyone anything, your labor was your own, etc. Morals? Values? Who needs them? At first, Rapture (Bioshock's location) was everything people dreamed. You could have whatever you wanted as long as you worked for it! No one said what was right and what was wrong! Then, like a house made of dominoes, it all fell apart. A society couldn't exist with that, and the purest proof was what happened to the people that made up that society. They discovered genetics, began to play with them, and started a race. A race to see who could be better then everyone else. It's hard to get what you want when you're neighbor has telepathy and takes it from you. So you get back by getting spliced with the ability to create fires and burn his apartment. After all, its about what you want and can earn right?
By the time you get there, Rapture is in ruins, and nothing is sane. Splicers are the most basic enemies you face, from start to finish. The constant genetic modifications they've put themselves through have driven most of them mad, and some of them know it. Some beg you to kill them even as they do their best to kill you and steal your stuff. Other mutter inane thoughts to themselves or fight with people that exist only in their mind, like one Splicer who reenacts a murder from his past (completely alone in a room) over and over again until you bother him. Every single Splicer is an individual who has completely lost their mind and sense of reason, and they did it to themselves.
What makes them so memorable is the range of responses you seem to find in them They're all crazy, and most of them know it. Some are broken shells, sobbing in corners and talking to dead figures from the past only they can see. Others have embraced it and enjoy their new-found "perspective" on life. Bioshock is an absolutely chilling game with brilliant social commentary in part due to the character and moral ground brought up by the Splicers. You pity them, and you fear them. Because they were human, and that means that if you're not careful, if you let yourself go to far, you could be one of them. A win for social commentary in a game, but an absolutely nasty enemy, especially in terms of the mind games it plays. Image source: Popfan
The Husk: Mass Effect
Verdugo: Resident Evil 4
You still don't see it then. You know it's there, you can hear it crawling around on the ceiling, underneath the catwalk, and periodically it's tail will lash out at you, making you dodge, but you don't see it. Until it locks the door and leaves it and you in a room together, upon which it comes out to play.
That's when you discover the other terrifying thing about the Verdugo: It is quite possibly the most immortal enemy in any Resident Evil game, or most games period. Even if you have the almighty RPG, famous in RE games for being able to one-shot any enemy or boss, the Verdugo takes the hit and...whats that? He's waving his finger at you, mocking you for even trying. Bullets bounce off him. Grenades don't scratch him. What are you supposed to do?
Run. And that's what most players do the first time they face this thing. Run like a coward, and get to the elevator and safety, leaving the Verdugo to whatever whims it has. Only a quick-minded player will realize that they can tip over a few cans of liquid Nitrogen, encasing the Verdugo in ice and thereby making it actually take damage, but it's still hard to kill the thing, and realistically the only way you can is either with Nitrogen plus an RPG, or some of the games incredibly overpowered secret weapons, none of which you'll have the first time through.
The Verdugo has one more level of nastiness that needs mentioning. Capcom got it's movement down right. Rarely has any game creature simply oozed a level of predatory grace, deadliness and menace. Verdugo is nasty, but also a great and memorable enemy. Image Source: Resident Evil Wiki
Regenrator: Resident Evil 4
Their ability to regenerate is only matched by their determination to get you. They don't stop. Ever. Shoot off their legs? They crawl. Shoot off their arms? They flop, the head hissing at you until something regrows. One armed, legless headless torso pulling itself toward you? Now that's the stuff of nightmares.
While you pretty much had to kill the first few through accident, the game eventually lets you in on how to kill these things (it involves a Thermal scope), but until then, you're only hope is to try and deal as much area damage as possible and hope you remove the nodes responsible for the regeneration in the process. As long as one is left, it will keep coming. And coming. And coming...
Like the Regenerator, the Reaper is capable of quickly regrowing any portion of its body. Limbs can be shot off, but that's a small worry for something that will regrow them in seconds. A decent chunk of it is entirely bulletproof to all but the most armor piercing of weapons. But it has one weakness. Unlike the Regenerator, the core parts of this bug (which allow it to regenerate) are on the outside (see the white patch there?), so you can clearly see what you need to shoot. I guess they're lungs, because they contract in and out as if it's breathing.
Ordinarily that'd make the Reaper pretty easy, but since it has armored coverings that slide over as it breathes out, unless you've got some heavy firepower on hand you're not shooting them. To make it worse, even if you destroy two of them but miss the third, the Reaper can regrow the other two. Oh, and it has a natural defense against you ever hitting them. Reapers emit a gas which messes with your vision and distorts the air around it like refracting water. So half of the time, you're gambling when you shoot at it, as the whole area around the Reaper is rippling and bending constantly. All of these features add up to make the Reaper one of the nastiest enemies I have ever faced, in any game, ever. Fortunately, unlike the Verdugo, a single RPG will kill them, but it says a lot when you're spending a decent chunk of cash to get an RPG just to dispose of one enemy.
What are some nasty enemies you guys have faced?