Nightmare Fuel / Scooby-Doo and Guess Who?

• In "Quit Clowning", we have the ghost of Pazzo The Clown. While still fairly comedic, he's also actively trying to kill the gang and Kenan Thompson due to them trying to save the show. And then there's the laugh.
• The Screaming Skulls in "Elementary, My Dear Shaggy", a burning, glowing green mass of skulls that chase down and somehow apparently eat anyone unfortunate enough to be in their way, even having a laugh similar to the Spooky Space Kook from Scooby-Doo, Where Are You!.
• "Too Many Dummies":
  • Even if they weren't the culprits, the mother and son doll collectors are outright terrifying.
  • Crazy Karl. Just for starters, he looks rather like the Joker, but with telescoping limbs. Scooby finds him so creepy that he digs a hole and buries him...and then he reappears while Scooby and Shaggy are staying in the hotel, taunts them about the dark, and says they should be afraid of it.
• In "Now You Sia, Now You Don't!", Sia's doppelganger provides a lot of Jump Scares when she keeps popping up out of nowhere as soon as Shaggy turns off the lights, which is not helped by the intense music accompanying it, and then disappearing when he turns it back on.