Harry Potter and the Deathly Hallows by J.K. Rowling: Bathilda Bagshot was dead the whole time (and is actually a snake)
The Harry Potter series was pretty messed up to begin with. Remember when Harry burned Quirrell’s face with his bare hands? Remember when Harry stabbed the Basilisk with the Sword of Gryffindor at the tender age of twelve? What I’m saying here is we are all culpable. We all let this happen. J.K. Rowling kept upping the stakes, and we never said boo.
In Deathly Hallows, Harry and Hermione meet up with Bathilda Bagshot. They’re desperate for information and hoping she can help. Turns out the famed historian has actually been dead for months, and Voldemort’s pet snake, Nagini, is using her reanimated corpse as a puppet. This is a level of bizarro horror that had me personally thinking fondly of the good old days, back when all we had to worry about was Voldemort slurping unicorn blood in the death forest.