When we go into non-horror games we don't really expect anything remotely creepy or worse yet frightening. However, there have been quite a few non-horror games where we've run into moments we didn't expect to make us want to play with the lights on.
Like Super Mario World, where Mario reaches the Valley of Bowser. Quite menacing on it's own, but then we reach the fight with Bowser. As a kid I didn't expect Mario to have to fight someone who dwarfed him, with a roaring thunderstorm and hellish music in the background.
Super Mario Bros. 3 was even worse, as when you reach World 8 it's a perfectly painted paralel to hell itself. The floating skulls and background music (made scarier in the Super NES version) don't help. Thankfully it becomes less scary when you fight a rather unintimidating Bowser at the end (who seems to forget the law of gravity).
And need I even remind you of the Mad Piano from Super Mario 64? -_-
So anyway, what are some of your scariest moments in non-horror games?
Some days I just blow up.