- The entire Yevonite religion for the people of Spira is one long exercise in Religious Horror and Existential Horror. Basically, the church is run by nihilistic ghosts who use dogma and assassination to keep the masses ignorant, blindly obedient, and prejudiced against any who would incite change or technological progress like the Al Bhed and serve Sin, the religion's equivalent of Satan bent on ritually destroying Spira that's being controlled by the braindead disembodied spirit of Yu Yevon, the religion's equivalent of Jesus. The church officials ritually send summoners and their pals on a pointless pilgrimage where they are to serve as a Human Sacrifice to temporarily delay Sin until it resurfaces again. The church also lies to followers by assuring that blind obedience to its teachings will allow Sin to disappear for good. This practice has been going on for a while and no one but the protagonists seem to care as long as it gives people a sense of false hope. Disturbingly stated by Maester Mika:Mika: Men die. Beasts die. Trees die. Even continents perish. Only the power of death truly commands in Spira. Resisting its power is futile.
- Yunalesca's profoundly creepy One-Winged Angel, where her hair of all things has the ability to manifest into a gigantic, Medusa-like head, complete with a horrible wail.
- Anima, who is also depicted above◊. Just... every last thing about her. A massive, twisted humanoid giant, chained and hideous. Its appearance is disquieting, but the real nightmare fuel comes when you learn what Anima is: Seymour's mother, who gave herself as Seymour's aeon because she saw no other way to redeem Seymour in the world's eyes — and later, when Seymour made his FaceHeel Turn, she couldn't stop him from using her as a weapon. Now look at Anima again, and see the pain and helplessness in her face... and then watch her Overdrive, and see her anger...
- Seymour summoning her in Luca. When she kills the monsters in the arena, she's crying tears of blood! Her mannerisms are also pretty heart-rending in a disturbing sort of way.
- Speaking of Anima: Baaj Temple, the abandoned, ruined temple you can find her at, and also which Tidus ends up at after being removed from Zanarkand early on in the game. Creepy music and absolutely no one present save for the resident Fayth (the aforementioned mother of Seymour) as well as Geosgaeno, which terrorizes Tidus at the beginning of the game and nearly succeeds in swallowing him.
- Watching Crusaders get reduced to black particles at Operation Mi'ihen is extremely disturbing. Then Tidus does their autopsies if you examine the bodies.
- Once you finally get inside Sin, there's a cutscene where the characters marvel at how surprisingly beautiful it looks in there... then suddenly it turns dark, an Evil Laugh is heard and you see a brief-but-horrible extreme closeup of Seymour, complete with Giant Eye of Doom.
Nightmare Fuel / Final Fantasy X