Nightmare Fuel / Onimusha: Warlords

• The music that plays in the keep.
• The Journal written by the painter Saimyou: It goes from telling his horrifying experience as he tries to escape the Genma, and slowly sinks into madness when Saimyou contemplates eating the human remains left by the Genma to survive, rationalizing that dead humans revert to meat, to downright praise the sight of artificially-produced demons and the Gates to the Underworld. It makes you realize that those dead soldiers got away with it lightly.
• The design of the Reynaldo: creepy beady eyes, extremely long rubbery tentacles, bladed appendages they can use to shank you if you're caught and the fact that their midsection is a gaping, toothed cavity. And to cap it all, the buggers can multiply if cut in half, like an amoeba.
• One of the underground rooms is filled with giant glass tanks containing what looks like humans... only for a number of them to break, releasing the growling Longarms inside.
• Hecuba transforming into her true form: involves her eyes boiling out of her skull and growing like a tumoral mass to envelope her entire head and her massive wasp abdomen seemingly expelled from her vagina isn't a good sight either. Not to mention she comes this close to killing Yumemaru while transforming.
• The doll boss Ayame from Genma Onimusha, a horrifying floating partially broken nearly invincible bell ringing monstrosity.