Nightmare Fuel / Adventures of Sonic the Hedgehog

  • A few of Robotnik's Villainous Breakdowns can amount to this simply because of how wrathful he can get. His red irises and tendency to growl and/or gnash his teeth don't help.
    • A particularly nasty one occurs in "The Little Merhog" after Robotnik gets his ass kicked by the periscope going up and down too quickly. He has quite the deranged expression on his face.
      Scratch: {quite nervous} Boy, that's what I call a look that could kill! {He laughs nervously.}
      Robotnik: {sporting a demented and angry Nightmare Face} It's not the look that will kill you. IT'S THIS! {He grabs and proceeds to thrash them both.}
  • Mama Robotnik is quite a disturbing and menacing presence due to just how vicious and monstrous she is. Robotnic's fear of her is completely justified. As Wes Weasley rightly put it on one occasion, she makes Robotnik seem "as meek as a lamb" by comparison. To say nothing of how she routinely escapes prison, breaking right through the walls and later storming directly into her son's fortress unhindered.
  • Katella the Huntress is pretty damn scary in her own right. Past her attractive appearance, she's a ruthless poacher who kidnaps sapient beings and sells them off to zoos. And she is able to essentially vanish them, one by one, without being seen. And that's not even counting how vicious she is towards those she likes, let alone loves. Let her rough treatment of Robotnik and his utter fear of her stand as proof of that. Even worse, although Sonic manages to free her Mobian hostages, Katella's a Karma Houdini by the end of the episode and still at large, setting off to abduct more people.
  • The climax to Robotnikland has this in the form of a haunted roller coaster, the afore mentioned Hellevator, a grotesque landscape with demons laughing at the villains, a door that sends them into a torture hall, Scratch's shadow getting decapitated (and putting his head back on!), a hallway of axes (where Scratch pulls out his heart), and fire breathing Badniks. The facade of this nightmarish landscape? Sonic's head!
  • "Spaceman Sonic" features a rather freaky slime alien thing. While it has some Nightmare Retardant moments due to its cold, it nevertheless is a Cyclopean monstrosity that seeks to eat Sonic and Tails after having nothing for thirteen years.
  • Scratch and Grounder melting in Birth of a Salesman while still conscious!
  • Sonic gets turned into stone (or at least encased in it) in at least two episodes. Imagine what that experience is like.
  • In one episode, Sonic has to decide if he wants to free Tails or people who got captured. He has to deliberately lose a race to get Tails back. While he was sadly trudging along, you hear Robotnik repeatedly yelling "YOU'LL NEVER SEE HIM AGAIN!" And it's echoed.
  • Though Unwilling Roboticisation isn't a horror visited as much as in other series there have been a few cases of Robotnik robotising unwilling specimens like Blackbeard the pirate, a whale, a pterodactyl and worst of all innocent little Beans in Dr. Robotnik's Mean Bean Machine.
  • "Mass Transit Trouble" has a particularly disturbing moment where Scratch sadistically fantasisizes about blowing up Sonic and his bones then falling into his burial hole in the ground.
  • "Tails' New Home" has Robotnik making robot parents to capture Tails. Sonic only figures it out when he realizes they kept calling him "Tails", not "Miles", his real name.