Conan the Barbarian/Nightmare Fuel

From Howard's stories directly to your bad dreams!

The Slithering Shadow/Xuthal of the Dusk: Let us introduce you to Xuthal: a palace-City in the middle of an endless desert, inhabited by depraved Lotus eaters that tend to look dead most of the time. And what about its god, Thog? The child of a Blob Monster and an Eldritch Abomination made of darkness, so dazzling that it's impossible to look at properly. Oh, and he frequently wanders the corridors of the palace looking for prey. And judging by Thalis' fate, being captured by him is NOT pleasant.
The room with the hidden Giant Spider in The Tower of the Elephant.
- On a similar note, Conan and the Spider God: a dungeon inhabited by a bull-sized Tarantula and her children.
Homophobia aside, Tascela from Red Nails is a disturbing character with heavy Psycho Lesbian tendencies. Not that the city itself is better: a giant palace infested with murder-obsessed psychos, monsters and forbidden secrets...
The monster summoned by Thoth-Amon against Ascalante in The Phoenix on the Sword: Part mummy, part ape, and so monstrous that it can destroy the soul of a man just by gazing into his eyes, as happens to Ascalante and almost happens to Conan himself. Even Thoth-Amon doesn't look at it directly.
The Gray Apes in general and similar monsters all have the bad habit of appearing with the most horrifying background in the stories. Especially Thak in Rogues in the House, who Was Once a Man.
The restless giant slug in The Hall of the Dead is quite jarring: it can't be killed by conventional means, never tires and spew acid.
The wraiths in The Castle of Terror are quite pitiful at first... then they go One-Winged Angel and merge into a giant, monstrous multi-headed thing with claws and legs which proceeds to slaughter a group of Stygians in a Grand Guignol-esque fashion.
The boar-like demon in The Snout in the Dark.
Khosatral Khel, the titular The Devil in Iron. The whole part when Conan is in his palace and must rescue Octavia sounds like a written Survival Horror against an invincible enemy.
The many horrors of The Scarlet Citadel, including a Blob Monster with tentacles and a toad-like head. Oh, and it cries and laughs like a mature woman.
- How about the scene where Tsotha-lanti boasts that he's going to skin King Conan's concubines alive and turn their flesh into scrolls upon which he will document his triumphs?
Akivasha and her unseen cohort of night horrors in The Hour of the Dragon.
- From the same novel, the Ghouls in the forest and the four Khitans with their deadly staves.
Conan's encounter with a Kraken in Conan of the Isles is of the worst kind, but then enters a giant shark.
The finale of The Dagger of Flame, where a horde of ghouls rise from the depths and take over the citadel, forcing everyone to flee.
The Black Stranger. Thoth-Amon must have taken lessons in Nightmare Fuel, seen how he psychologically tortures Count Valenso.
- There's also the harrowing scene where Valenso has his niece's protegee, the young girl Tina, savagely whipped because he thinks she is lying about the Black Man.
Thugra Khotan in Black Colossus: the darkest and most twisted example of a nightmarish stalker out there.
The people who brutally tortured and killed a demigod in Shadows in The Moonlight. The fact that they awaken to murder intruders when hit by the moonlight only adds fuel to the fire.
The women-things of the titular The Vale of Lost Women.
The People of the Black Circle: including the four inhuman sorcerers and the Master. Dear God the Master.
The creature from the "The God in the Bowl". Even more scary because it's not fully described, allowing you to imagine it's appearence...
The giant snake from the 1982 film, the ape man and the demonic god from "Conan the Destroyer", the Mask of Acheron (with its writhing tentacles and puckered mouth sucking up blood) and the massive aquatic beast the Dweller from the 2011 film... Let's just agree that if it's a movie of Conan, there will be a creature straight from someone's nightmares in it.