The Vortex Queen in Ecco the Dolphin. Thrust into a large black void with a huge alien skull floating there...I was about 7 years old, nuff said
T-002 from Resi 2, most often you couldn't see him but the moment you enter a room with him in you can hear the footsteps
Nemesis from Resi 3, purely for the speed element...you can't run away from it lol
As mentioned before, the "right-hand man" monster you need to freeze in Resi 4. Another speedy chasing type monster
Nothing in Resi 5 really...
Any of the murderers in Clock Tower 3...doesnt' help you play a small girl who has no weapons and panics even when they miss you with an attack, making it even harder to get away....v. atmospheric game
Cyberdemon from Doom 2
Alien Queen on the 3 boss levels in Alien Trilogy on PS1. Not scary in AvP as you can see em miles away. In AT the draw distance was about a metre...so it's like facehugger egg..egg...eggQUEENARGHH!!!!