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Nightmare Fuel: Watchmen
Watchmen helped redefine the comic book and lead the medium into a darker era. How? Large amounts of Nightmare Fuel. Alan Moore really is the master of this sort of thing.
"I WILL GIVE YOU BODIES BEYOND YOUR WILDEST IMAGININGS"- A perfectly innocent-seeming advert for the Veidt Method takes on Nightmare Fuel properties at towards the end of Watchmen when Ozymandias' plan to unify the world by dropping a gigantic "alien" monstrosity to kill half of New York is revealed.
The Squid Monster reminds many of the standard anatomy textbook diagram of the female genitalia.
The entirety of Tales of the Black Freighter. Even if you see the ending coming a mile away, it somehow just makes it worse. "In hell, at least the gulls are happy."
Rorschach eating beans freaks a few out for some reason. It just seemed so wrong. Maybe it was the sound effects... Ronch ronch ronch.
Lots of Rorschach's actions are seriously grotesque. But somehow the thing that really gets to many was that little throwaway detail of young Walter's drawing of his dream.
Rorschach's account of how he came to make his mask, boiled down into five rage-filled words:
Finding out what it was that made Rorschach the terrifying vigilante he is.
"...Stood in firelight, sweltering. Bloodstain on chest like map of violent new continent. Felt cleansed. Felt dark planet turn under my feet and knew what cats know that makes them scream like babies in night. Looked at sky through smoke heavy with human fat and God was not there... This rudderless world is not shaped by vague metaphysical forces. It is not God who kills the children. Not fate that butchers them or destiny that feeds them to the dogs. Itís us. Only us. Streets stank of fire. The void breathed hard on my heart, turning its illusions to ice, shattering them. Was reborn then, free to scrawl own design on this morally blank world. Was Rorschach.
The bit where Adrian opens up the vivarium dome and lets the snow in to cover the dead bodies of his three associates really hardcore unnerving. Mostly It can take more than one read-through of the comic before it even hits you as to what the hell just happened.
The opening pages of chapter 12, a wrecked, broken New York with the streets full of corpses, blood and 'alien' tentacles.