!!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.
* ''WesternAnimation/TheScoobyDooProject'' [[http://www.youtube.com/watch?v=uMsA6_Qh_jw  ]]. 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 ''WesternAnimation/TheThirteenGhostsOfScoobyDoo''.
* The musical cue that accompanies Captain Cutler's appearances in "A Clue for Scooby Doo".
* One from the classic show; episode 15 of the first season of ''WesternAnimation/ScoobyDooWhereAreYou'' features the Spooky Space Kook. The opening of that episode... We have an alien, dilapidated ship drifting eerily across the screen, and then the titular Space Kook, a lumbering spacesuit with a glowing, flickering skull inside its translucent dome, approaches, staring right into the viewer's eyes as it gives out this [[https://www.youtube.com/watch?v=swhAv9VcBWc horrible shrieking cackle]].
** Making things worse? The sound of the alien ghost-ship [[HeyItsThatNoise can be recognized as]] the "electronic rattlesnake" noise from ''Film/WarOfTheWorlds1953''.
** The sight of a walking skeleton in a spacesuit might also be [[HarsherInHindsight scarier in hindsight]] for [[Recap/DoctorWhoS30E8SilenceInTheLibrary Who]][[Recap/DoctorWhoS30E9ForestOfTheDead vians.]]