This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Death Masks
Shiro's death by torture.
Harry's been tricked by Nicodemus into touching one of the cursed coins, meaning he's now got a copy of a Fallen angel in his head. He's not about to let it start him tempting him, but just as he's about to bury the coin in the floor of his lab, a voice whispers in his head. It only says Harry, but it is nonetheless extremely creepy.
Barabba's curse. You can sentence one people to death, and that will be it although the Knights can take the victim's place, if they chose to. And it's in the hand of one of the vilest persons in the Dresdenverse.
The plague curse. It infects the victim with almost any known illness, making "the Black Death look like chicken pox". And it spreads through air. And it's released into a very busy international airport.