I tried playing Slender: The Eight Pages, with my friend but we couldn't even move the controls without freaking out. It wasn't Slendy that scared us, it was the music! Isn't that right @Julia Angeles?
Slender Game. Scary as hell. You should try this if you haven't already. Small download 56mb. In the dark, with a flashlight, some guy chasing you...oh ya, you don't see him except in the flashlight. Otherwise, complete darkness.