This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Everwild
The sequel to Neal Shusterman's Everlost, Everwild, involves mass murder of children, and the prevention of them reaching "the light". Also, this is done using possession, and the reader sees the the torture one man suffers when he was almost used for this, not knowing why he threw the small child who couldn't swim into the pool. There's also the 'buried alive' scare that is present in both books, as in Everlost, if you stand still too long, you sink into the center of the earth. Furthermore, in the second book, one of the main characters is slowly turning completely into chocolate.
The prospect of Everlost is nowhere near as frightening as the prospect of Mary Hightower. Everything that happens to her from taking to the skies in the Hindenberg, being brought back to life and dying again, to having her army of bodysnatching dead teenagers rebel against her only makes her more powerful and makes her seem scarier.
Anything that seems scary, will be. Oh yeah, there's the consolation that nothing can hurt you, but the various monsters of Everlost manage to come up with fates worse than torture and death including chiming, cramming, pushing down to the center of the earth, sealing in barrels, permanently sharing a body with someone, trapped in the body and mind of a wild dog, forced into the body of a breeding sow so fat that it can't move, and, perhaps the most common, becoming trapped in a rut endlessly repeating the same few actions over and over again. Worst of these are probably Milos and his search for the one eyed jack he knows will end him in a deck of cards and the pair of Neons who do nothing but tell knock-knock jokes, but had never heard of the interrupting cow.