Lesse...
Final DooM - Go 2 It. 'Nuff said.
Resident Evil 3 - Nemesis capable of running freaked me the fuck out the first time I played. I was like "A friggin' running tyrant!?!?!"
Resident Evil 2 - the whole "zombie arms bursting through the board walls, but that one gets everybody.
Resident Evil (GCN) - Crimson Heads. 'Nuff said.
Any Castlevania game from Symphony of the Night on up -