lol Dead Space enemy designs are taken right out of Blue Stinger on Dreamcast. Dead Space always seemed like a more serious and better version of Blue Stinger to me. Tho DS needs more Christmas music.

Anyway. I dunno, nothing really scares me in games. I like those centipede things in Dark Souls 3. Soulsborne has a lot of cool enemies, Bloodborne even uses simple giant spiders well. Silent Hill 2-3 have plenty of good ones. Also, I like the multi-armed lady in Evil Within.

I didn't get far into Blue Stinger however they definitely resembled Necromorphs. You could argue that Blue Stingers enemies were taken from System Shock (The original creators of Dead Space) But than again both System Shock 2 and Blue Stinger released the same year.

As far as Resident Evil goes, the Hunters were the ones that really scared me. Right from their introduction you knew they were serious business. First time through the game, I'd enter a room and pray I didn't hear the slow thud of their footsteps. Worse was when the sound of the footsteps picked up the pace, cause then you knew they were after you. And even then, the absence of footsteps didn't mean you were safe; they could just be hiding, waiting to dart out from behind a corner or something. Haven't even mentioned those screams either. They really made the return to the mansion and beyond a very nerve racking experience.

Not going to get into spoilers here. Play the game or watch a let's play.

I always thought it was funny how Final Fantasy VII had a moon that was supposedly the end of the world, but if you just let the game sit and not do anything, the Meteor will never fall. It only falls in the ending movie after you beat the last boss. (Sorry, spoiler, but by now everybody that cares has seen it.)

Majora's Mask has a meteor that really will hit the ground and destroy the world if you don't do anything.

The Arch-Viles in Doom 2 were scary until I figured out how to beat them without getting hurt. You'd hear a noise, and the next thing you knew you were on fire.

Goro from the first Mortal Kombat was terrifying. So was Eyedol from Killer Instinct. 

Obligatory mention of Giygas aside, the Mimics from 2017's Prey were a pretty good fodder enemy for a horror game, given that their main gimmick was imitating objects/items, which encouraged you to be paranoid about every little object in an environment.

The thing with the pyramid head

Also, the Xenomorph in Alien Isolation.

Making your way through the space station knowing it's out there stalking you, straining to hear or spot any sign of it before it sees you first, hiding under tables or in lockers to avoid it and being instantly chased down and murdered if you're detected, this thing was truly terrifying.