Magic: The Gathering/Nightmare Fuel

• Pretty much the majority of The Seer's Parables (except a few sections), which illustrates how lovecraftian Shadowmoor is.

"It burns
My brain

Oh heavens

How it burns."

• The flavour texts for Lord of Extinction, Spined Wurm, Sliver Overlord, and many others.
• Art on the original Torment version of Mutilate Some, however, may find it funny.
• Eldrazi bleed Nightmare Fuel.
• Macabre Waltz anyone?
• Hypnox.
• Phyrexia in general is an excellent source of nightmares.
  • Check out the art on Vivisection. Yes, that is indeed a human head split open and picked through while its owner is still alive.
  • The Phyrexian recruitment video contains a mix of electronic moans and surreal, gruesome imagery. All Will Be One indeed.
  • And the sequel video: Phyrexia won. Mirrodin is clinging just barely to life. The Father of Machines is coming.
    • The Phyrexians in the books are absolutely terrifying, having a disturbing fixation on perfection, and in some books, you see events through a Phyrexian's eyes. And in one case, you see a complete metamorphosis in perspective. Mind Rape through Body Horror and cybernetics eating your soul. There is the oh so subtle hinting in Planeswalker and Time Stream that anyone you know or love might just be a Sleeper who is waiting to call on the Negators. And let me tell you about Negators. Their appearance and fighting style lends heavily toward implanted weapons and other nasty things. They look like mishmashes of mummies and magitek. And any Sleeper can call on them. And some of said Sleepers don't even know they are one until a voice starts up in their head.
    • In New Phyrexia, the Negators got worse.
    • You may think that the fact that they are no longer mono-Black means factions of non-scary Phyrexians, right? I mean, how can White be scary? You're wrong. Very wrong.
    • Phyrexian Unlife. Unless it's combined with Melira, in which case it becomes hilarious.
• Grave Titan. A walking Zombie Apocalypse. Animated corpses crawl out of his chest. The Duels of the Planeswalkers 2012 promotional art is particularly chilling.
• The new block, Innistrad, is based on gothic horror, and the artwork doesn't disappoint. Just consider the chilling feel of Village Cannibals and the very aptly named Creepy Doll.
• The way werewolves transform according to the Planeswalker's Guide for Innistrad (the article about Kessig):

"The transformation process is harrowing for the lycanthrope and incredibly disturbing to any witnesses. The eyes change first, the whites darkening and the iris filling with color. The claws go next; the hands elongate, knifelike claws extend from the fingertips, and the thumb forms a claw back near the wrist. The muzzle thrusts forward out of the human's skull, and the teeth jut through the gums in sharp points. Bones crack as they rearrange. Marrow spills into the bloodstream as ribs and skull fracture and telescope. Thick, wiry fur pushes through the skin, often pushing out normal human hair. The tailbone elongates and becomes a shaggy wolf's tail. Metabolism speeds up, increasing blood flow, oxygen flow, and glandular production, creating cravings for protein and fat. Any clothing that was worn at the time of the change is generally torn to shreds and falls away. If a werewolf dies in beast form, it changes back to human form, a process called death reversion."

• Also from Innistrad--Sensory Deprivation. Plenty of Body Horror and Eye Scream involved.