The first El Gigante you encounter demonsrates its impressive strength by killing a bunch of Ganados right after they unleash him from behind his cage. The ensuing fight with him isn't any less intimidating - he uproots trees with his bare hands and tries to crush you with boulders the size of a minivan.
The Ganados once their heads begin to explode, causing the Plagas to sprout out of their bodies.
Dr. Salvador. Imagine a burly, chainsaw-wielding Ganado with a brown face mask resembling a potato sack, running at you with delirious abandonment, and you've got the idea. His primary method of attack is to swing the running blade of his chainsaw into the crevice of your neck, ripping your head clean off of your torso; needless to say, this is a one-hit kill. He is also very difficult to take down and often requires several bullets before even staggering backwards.
Not to mention you'll probably hear him before you see him... which means that you'll be hearing a chainsaw when you can't see anyone else.
The Regenerators. Seeing one lurch into view and stagger towards you, with an unholy, guttural sound like someone with razors stuck in their throat burbling from their maw...
Even worse, it almost sounds like it's laughing at you as moves in for the kill.
There are two potential first encounters with Regenerators, depending on how you go through the lab. In one scenario, you're exploring when you see a big gray corpse in a freezer. So you keep going, and when you turn back, it's GONE. In another, you find Luis's notes explaining what they are and how they're created... and when you put them down, you hear the door behind you slide open, and that telltale wheezing starts up...
Encountering the lab where they were created, finding the horrific failed test subjects, and ending up inside a freezer with numerous partially complete creatures hanging from the ceiling with parasites visible and still moving inside them once you turn the cryogenic device.
And then, once you've developed a healthy fear of the things, you find yourself in a hallway lined with jail cells on either side. And you hear the telltale rasping of a Regenerator. And you know it's in one of those jail cells, but you don't know which, and you know that if you check inside the wrong one, you'll turn around just in time to see it stepping inside from the opposite cell, blocking your only way out. It's actually past the jail cells and around the corner, in a position where it's unable to sneak up on you from behind at all.
Another interesting little tidbit: On Professional Mode, which isn't really that much harder than normal mode, they can run. And yeah, it's horrifying.
Iron Maidens, as seen in the page image. They're Regenerators that can stretch their arms and grab Leon, impaling him with their spikes. Hence the name.
Iron Maidens also twitch constantly, and if you shoot their legs off, they don't flop forward like normal Regenerators. They slither.
If one of them grapples Leon, you get a nice close-up of their face practically opening up as it chomps down on him. Absolutely chilling.
Think Regenerators are harmless once you've taken out their legs? Think again. The bastards can still lunge up and bite you in the neck if you get too close.
The Comillos, which are essentially wolves infected with Las Plagas, have a horrific transformation of tentacles popping out of their flesh, and savagely attempt to rip out your throat/bite your face off when they attack you.
Provided you didn't double back across the lake at night after facing the Del Lago, your first encounter with the Comillos will be walking up a path at night while a pack of Comillos wait for you. You can actually see them, sitting perfectly still with an evil snarl on their faces, waiting for you.◊ It's ten times worse if you spot the Colmillo's silhouette in the distance and assume that it's your canine buddy who just helped you beat El Gigante not two minutes earlier; Mood Whiplash at its finest ("Oh, hey, doggie! Who's a good b—AAIIEEEEEEEE!!").
You also encounter them later on, wandering around the hedge maze in Salazar's castle. Hearing them panting from a distance without knowing their exact whereabouts in the maze is frightening enough as is, but the fact that they tend to pop out of nowhere and can even come up behind you makes this one of the more nerve-wracking segments of the game.
The first time you see Las Plagas in its natural form. During a "dark and stormy night", Leon enters a small canyon and sees one of Ganados approaching him, twitching and convulsing in a way the player hasn't seen before. The effect is somewhat chilling because the Ganados' eyes are glowing. But then it gets downright horrific when its head bursts apart and a fleshy mass covered in squirming tentacles and eyestalks emerges from Ganado's neck. Its main tentacle is tipped with spikes that only require one or two hits to kill Leon. And through all of this, it's smiling at you.
The centipede-like plagas that spout from Zealots are perhaps even worse. They erupt from the host's mouth and cause their head to tear open at the jaw and hang behind their back, and the huge, squirming parasite can bite Leon's head clean off if they get too close.
Ramon Salazar's first scene, and all you can think is "What the hell is that guy?"
Del Lago, should you decide to shoot the lake repeatedly before engaging in the actual boss fight, will erupt from the lake and close its massive jaws over Leon and most of the dock in a single bite.
Speaking of Del Lago, getting knocked off the boat and swimming to safety as the creature encroaches from behind is always terrifying. The further away from the boat you are, the scarier it is. And even after defeating the thing, you're still not in the clear. Your foot gets caught in a rope that is attached to Del Lago's sinking carcass - and unless you cut quickly, it'll drag you down with it.
Aptly referred to as "It" by Saddler, U-3 is a disgusting abomination with a broken jaw, serpentine spear-like tongue, deformed body, and crazy eyes, among other things. And you have to outrun it in a large cage with narrow corridors where it can attack you from the ceiling as well. After you get through the cage, you enter into the second stage of fighting with U-3. If the creature gets a good enough shot at Leon with its pincers, it can give him what the medical community likes to call a hemicorporectomy - in layman's terms, he gets cleaved in half at the waist. If successful, this is a one-hit kill. Not a pretty sight...
And then when you enter the second phase of that fight, you manage to kill U-3's host body but the giant parasite keeps fighting you anyway, while dragging the limp torso around underneath.
The Garrador. Being trapped in the prison cell with the the first one is bad enough, but later on you fight two at once! And their eyes are sewn shut. Be thankful they dev were merciful enough not to go with their original plan for the two Garradores; the chamber you fought them in was supposed to be pitch-dark, with the only illumination coming from the lamp on Leon's belt.
That charging thrust Garradors make at you? Taking a lethal hit from that results in one of the more brutal deaths in the game: he stabs Leon through the face and lifts him up by his head, Leon screaming horribly all the while, and finishes by shoving his other claw under Leon's ribs.
The fight with Bitores Mendez. The guy, who is freakin' HUGE, somehow sneaks up on you, starts to strangle you, throws you against the rafters, and proceeds to lock you in by bending the door handles with his BARE HANDS!!! He then tries to grab you again and snap your neck like a matchstick, but you get out of the way and knock over a barrel of gasoline, shoot it so it catches fire, and get away and all the gasoline blows up. But then, of course, the smoke clears, you see his body fall apart, revealing a long, thin hand with giant claws!! Then you see him, standing there, before his torso detaches from his legs, growing a giant spine and a pair of segmented limbs.
There's a room in Salazar's castle where you have to sort paintings. The paintings are grisly portrayals of hangings and lynchings, showing that he is sick (probably more so than other Resident Evil bad guys).
From a quick comparison to the scene where you see how the Plagas inside Leon and Ashley are destroyed, the Illuminados emblem seems to be the image of a Plaga as it latches onto the victim's spinal cord.
This game has some Nightmare Fuel as a Bilingual Bonus, no less. The zealots' phrases get pretty creepy, specially the tone in which they are said: "Morir es vivir... Morir es vivir..." ("To die is to live...to die is to live...") and "¡Oh, sí! ¡Quiero matar!" (Oh, yes! I want to kill!) deserve a special mention.
If you get killed by a Novistador when it grabs you and starts puking acid on you, you'll be treated to a disturbingly realistic sight of Leon with half of his face melted off. Also, the music during the first encounter with them in the sewers (link above) fittingly sounds like a swarm of giant insects.
Toward the end of the game, a filthy red dumpster can be seen near some jail cells. When opened, it contains a dirty, blood-stained bodybag, which suddenly begins writhing about violently. This does not attack the player in any way, but if encountered at the wrong time can change garment colors and deteriorate sanity. Taken Up to 11 in the bonus game Separate Ways in post-GameCube version, where the dumpster is already opened and the bodybag is thrashing about with significantly more vigor even before the camera pans down to the bottom. The character Ada simply looks disgusted and shuts the lid. The player... probably not as much.
The final illustrations showing what happened to the villagers: The music goes from quaint and upbeat to ominously chilling as we see men from Los Illuminados herding everyone into the church, a man is held down while Saddler's minions ready his injection, another man faces away from his concerned family with a demonic look on his face, a small child sits in a high chair either dead or dying while her indifferent mother stands nearby, a crowd gasps in horror as a parasite rips its way out of someone's throat and his head hangs off to the side...
While the normal Plagas' habit of blasting out of their hosts' heads is pretty disturbing on its own, this◊ collection of scrapped concept ideas look like they've been plucked straight out of a Junji Ito manga.
During the short segment where you control Ashley, you are left completely unarmed and the only thing you can use against your enemies are lamps that Ashley throws but even then, it's not enough.
The worst part is after you get past the Zealots. You descend into a dark room, a creepy drone constantly playing in the background, the only source of light coming from Ashley's flashlight, and in there, you see various armor statues scattered around the place. Eventually, after solving a relatively easy puzzle, you enter a room where you obtain the serpent ornament. And then, after hearing some mechanical noises, all you hear is the noisy clanging of the now conscious Plaga-infested armor statues, coming to get you.
The Boss fight encounter with one of the two Verdugos (the two hooded B.O.W's that act as bodyguards for Salazar) in the castle's sewers. Everything about it is nerve-wrackingly intense considering the circumstances. 1. You're in an enclosed space so avoiding it is almost nigh impossible. 2. You have to wait for the elevator to come down, that feels almost like an eternity since you're having to dodge and flee the persistentabomination at every given turn and finally 3. Is using whatever firepower you have against it.... that doesn't do any good except piss it off even more. And God help you if you use up the few scattered nitrogen canisters or even miss that one single shot with your Missile Launcher.