!!If you're looking for examples related to a specific show or movie, see these:
* ''NightmareFuel/ScoobyDooOnZombieIsland''
* ''NightmareFuel/WhatsNewScoobyDoo''
* ''NightmareFuel/ScoobyDooMysteryIncorporated''
* ''NightmareFuel/BigTopScoobyDoo''
* ''NightmareFuel/ScoobyDooHauntedHolidays''
* ''NightmareFuel/ScoobyDooWhereAreYou''
* ''NightmareFuel/ScoobyDooFrankencreepy''
* 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.
* In "To Switch a Witch", the townsfolk decide that a friend of the gang is a witch and were going to torture her to make her confess, Salem-style. Shaggy and Scooby take the brunt of this, which could have gone worse were they not MadeOfIron. Sure, the squire who was the ringleader briefly apologized, but none of those responsible were prosecuted for what amounts to assault.
* ''WesternAnimation/TheScoobyDooProject'' [[http://www.youtube.com/watch?v=uMsA6_Qh_jw [1] ]]. It's a parody of ''Film/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 Ghouls getting [[BrainwashedAndCrazy Revoltized]] in ''WesternAnimation/ScoobyDooAndTheGhoulSchool'', specifically their expressions: Sibella's eyes [[WideEyesAndShrunkenIrises shrink as if she were going feral]], Elsa looks like her mind just got fried, Phantasm quickly loses her GenkiGirl composure and scowls for the first time in the whole movie and Winnie howls for some indiscernible reason. Elsa, Winnie and Tanis were freed early, but Sibella and Phanty remained under the spell longer. The former was freed by Tanis and apparently needed a few seconds to shake off the effect. Phanty, being under the longest, probably would've had more permanent effects had Scooby not knocked over random chemicals in the potion.
--> '''Tanis:''' Gee... you were under the hairdryer so long, you were getting cranky.
* In one of ''The new Scooby-Doo movies'' episodes, the gang helped Creator/DickVanDyke discover that his circus was being terrorized by the strongman, sneaking up on the guy while he's working out. But the strongman reveals that he not only heard them, and demonstrates what he'll do to them by effortlessly twisting his barbel like a pretzel. This is not the usual greedy Scooby villain; this guy intends to straight up ''murder'' the gang.
* The Jaguaro from "Jeepers, It's the Jaguaro" is pretty tame, considering it's an ape monster with a cat's head, but the screaming sounds it makes are terrifying.