"Don’t tell me what I can’t do."
Setting: Magicians know how to summon spirits, and for a price, bind them to their will. Spirits are wonderfully versatile and ask for so little in exchange. Spirits of greed can give you money, while a wolf spirit can make you into a vicious predator. Spirits you have bound are easier to control, and someone else's bound spirit is harder, but failing to properly bind a spirit correctly can mean that it misinterprets or disobeys your commands, or even worse that it screws things up. In short, you play a person -- a normal person -- who knows how to summon and bind beings from beyond for personal purposes. The question is: can you handle it? Where do you draw the line when you see what other magicians are doing?
Characters: PCs will be ordinary people who have stumbled upon how to summon otherworldly beings and make deals with them. Given how spirits fued with each other, the prices that they ask make other summoners potentially dangerous threats, thus the PCs will find banding together for safety essential to their survival.
Game System: World of Darkness, Unisystem, or GURPS