Nightmare Fuel / The 13 Ghosts of Scooby-Doo

• The townsfolk (plus Daphne) turning into werewolves in the premiere episode "To All the Ghouls I've Loved Before".
• "Me and My Shadow Demon" has a creepy scene where Vincent Van Ghoul's facial features are scrambled while he's yelling at Flim-Flam from the crystal ball.
• The Bad Future in "It's a Wonderful Scoob" where Flim-Flam and Scrappy have become Time Slime's motorcycle-riding minions, Daphne has been enslaved and has aged horribly, and Shaggy has gone insane while clinging to the futile hope that Scooby will come back to save everyone (yet doesn't realize that Scooby's standing right in front of him).
• The fact that Captain Ferguson (the sixth ghost) and his passengers from "Ship of Ghouls" are actual ghosts who died in a Titanic-like disaster 50 years ago, and want to share their fate with living people. The way the cruise ship Queen Myrtle sails through the fog to show its true form (a floating wreck) is quite disturbing, too.