!!If you're looking for examples related to a specific show or movie, see these:
* After watching "Vampire Bats and Scaredy Cats" (''The Scooby-Doo Show''), this troper, as a young child, had to sleep with a full head of garlic on her nightstand. ''For a month''. Literally had nightmares about vampires coming to kill her.
* [[http://www.youtube.com/watch?v=uMsA6_Qh_jw The Scooby Doo Project]]. It's a parody of TheBlairWitchProject. That should show give you a good idea. [[spoiler:What makes it worse is it's implied the gang ''died'' at the end]].
* One classic ad on Creator/CartoonNetwork featured characters from WesternAnimation/ScoobyDoo: Shaggy showed up in a spooky castle calling out, "Scooby-Doo! Where are you?" This cut to Scooby on a tropical beach, saying, "Right here, Raggy! On Rartoon Network!" What was scary about it was not only the notion that Scooby would desert his friends in the middle of a case, but also the fact that Shaggy was barely animated at all, paralyzed and semi-slouched in seeming defeat as he called for help. It was ''haunting.''
* The townsfolk (plus Daphne) turning into werewolves in the first episode of ''TheThirteenGhostsOfScoobyDoo''.
* The musical cue that accompanies Captain Cutler's appearances in "A Clue for Scooby Doo".