This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Life on Thedas
In chapter 7 the narrator is in the middle of being dragged off to a Fate Worse Than Death - life imprisonment in Aeonar. Still shaken from realizing he's a mage and an abomination, all he can do is scream helplessly for Elisa to help him.
In chapter 11 the narrator wakes up in the middle of the night in Denerim. And he killed eight people with his bare hands. And Leliana. Apparently.
The demon deliberately screws with the narrator's mind to try and weaken him. It certainly works. Highlights include showing him strapped down in an insane asylum then ramming a needle in his eye.
The narrator uses blood magic to take control of Zathrian, and only just manages to stop himself forcing the elf to ram a sword through his own chest.
In chapter 18 we finally see the demon stretch its legs. And it murders everything.