My first one.
Manga/Anime: Hunter X Hunter
Ability: The power to grant practically any wish. (there is a catch of course)
Description: Sometimes Alluka will ask 3 pesterings (request) of a person, they are generally simple things like giver her a piggy back ride, or play a game with her. If a person manages to fulfill 3 of these request, they are then allowed to request a wish from Alluka, however, if the person were to instead turn down4 of her request in a row, they, and their most loved one will die instantly.
Sounds simple tight? But there is more!
The difficulty of Alluka's pestering s depends on how big the wish/request of the last persons was. Also, if the last wish was an extremely difficult one, and the next person fails their pesterings, more people than just the person, and the loved one will die.
Example: One time a person asked Alluka to make her a billionaire, and it was fulfilled.
But the next person Alluka pestered was given some nearly impossible request.
Her request were: "Can you give me your liver?" "Can you give me your spine?" "Can you give me your brain?" etc.
Need less to say, the person failed the pesterings, and she and her most loved one died, including 67 other people due to the enormity of the last wish. After you and your most loved one die, they other people are determined by how much time you've spent around them, so these will most likely be people like your classmates in school, people you lived with, etc.