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Nightmare Fuel: Dracula
The description of the Count crawling out of the window and across the stone wall (with several hundred feet of sheer cliff face below it) and into another window is terrifying.
Nightmare Retardant: Until you realize what gravity would do to your cape and clothing when you are upside down...
Dracula's mortal minions laughing at Jonathan's predicament when he looks to them for help, and turning the correspondence he entrusted to them back over to his captor.
That village woman coming to the castle to demand her baby back. After the Brides already ate him. Shouting abuse at the helpless Jonathan, who doesn't pity for her when the wolves come since he feels that her fate was better then finding out that the vampire women had devoured her child.
Renfield, in a moment of clarity, begging to be removed from the place where he can do most damage in his madness, only to be utterly dismissed by the heroes.
Dracula's metaphorical rape of Mina — which only gets worse when she has to re-tell it from her point of view — is especially graphic and chilling.
How quickly and brutally the men turn on Vampire!Lucy, calling her "wanton" and "voluptuous" and talking about how "impure" she is now before crowding around her and hammering a three-foot long and three-inch thick wooden stake through her chest, leading to one of the goriest portions of the book, is dripping with misogyny and Unfortunate Implications. College discussions on this scene draw parallels to gang rape, honor killings, and violence against prostitutes in Victorian times.
Dracula sucks so much blood from Lucy that even her gums are rendered pale!