Monkey Island 2: LeChuck's Revenge/Nightmare Fuel


 * LeChuck chasing Guybrush around is terrifying. While you're desperately trying to solve the last puzzle of the game, there's this dread that at any point, LeChuck could come in and send Guybrush screaming in pain into the next room. For a little kid trying to finish the game while watching the loveable pirate being tortured, this game is an anciety-inducing masterpiece.
 * Guybrush's parents come back in his dream, and then their skin melts off. Then the scene goes funny again when they start dancing. But the scene goes scary again when LeChuck shows up, turns into YOU, and then kills you the same way you killed him in the first game. It's not exactly The Exorcist, but it can be pretty freaky when you're a kid.
 * The first time you enter the bolted tunnels under the waterfall.