Hello, there. I am a Baron von Loane
I am a wielder of great magic. So great in fact that I can bend reality to my whim. However, after having my fun and spending almost a century fucking with this world (Sometimes literally) I have grown bored with my powers. To put it simply, If I desire food, I can get it instantly. Same with drink, company, sex, money, power, and any other valuable thing that you or I can think of.
I almost went insane, until I came about a solution to my apathy problem. Thus I created the DEVIL'S CHALLENGE.
I'm well aware that my situation is enviable to the downtrodden, so I lend my services. I have a little place and people come to me with their wishes and I grant them. To an extent of course, I won't give anyone equal power to my own willy-nilly, and I won't waste time on something like gaining wealth. I grant impossible wishes like wishes for love, changes to one's body, and a surprising amount of things that relate to sexual intercourse.
But it isn't called a challenge for nothing. I will grant them their wish, but in the form of a curse. If a woman were to wish for longer hair, I would make it grow quickly and endlessly until she fulfilled some task. Typically addressing a flaw those shitty genie wishes tend to cause. If they succeed, they gain full control. In hair-lady's example, she would have complete control of how long it was and how quick it grew.
The only other way for the challenge to end is through Death. In my prior example, the lady gets stuck in a room and her hair increases to the point where she gets crushed to death.
I just sit back and watch. Specifically I enter the mind of those who take the challenge so I can hear their thoughts. I do this silently, since there is no real point to me messing with their chances. Rarely do my challenges last longer then a day as I like to craft the curses as quick kills. Not necessarily painless, or quick for the player, but I don't want to spend a week in someone's head.
Today is no different. Someone enters my office, cloaked and in baggy clothing. They already know what I do and why they are here.
They speak their wish.