from Psychonauts. The theme itself isn't that terrifying, unless the idea of circuses themselves freak you out, which they do me... but this level combined a circus with a butcher shop in some hellish nightmare in which adorable bunnies get ground up into meat monsters.
from DKC2. It's freaky and haunting while still being fast-paced and energetic. Gets your heart pumping for an exciting level, the only one of its kind in the game. Indeed the track is only used once, making it stand out all the more.
from Super Mario World. This was my first game ever, when I was 3, so its music is wound into the very fabric of my being. And I'm pretty sure I still hear this song in my nightmares. Of course, I love the haunted house theme too, but this one is even creepier, with its background arpeggiation, threatening chords, and sudden powerful hits. Truly a classic.But what takes the cake...
from Donkey Kong 64. As a trembling little eight-year-old girl, I would NOT play this level unless my parents were around. The endless dingy corridors and the possessed red-eyed Kremling robots that ran after you and then, just when it seemed they were about to seize you, would suddenly freeze in their tracks and have to rewind themselves, terrified me. But what really set the atmosphere was the creepy music. Listening to it today still makes me tense up, which is kind of silly, but this level will always retain somewhat of the nature of Hell that it had for me when I was younger, a place where toys try to kill you and childhood fun goes to die.