power of the soul, spirit fushion Options

Iv been wondering and this is just a strectch if there is such an art of mystic ability that allows a normal human to bond his spirit with that of the fiends around him the devils that are in physical form would it be possiable for a person to be able to hold the spirit within themselves and then use it when ever they want with a degree of negetive effect but still im just wondering iv seen it done is some bits of fiction and also have read in some obscure mystice works that it is possiable i would just like to hear from others and if so how to do it would not mind learning myself

Certainly i believe it can be done, but i agree with BB3 that a low entity is really the used car salesman of the spirit world and anything with enough power will probably pull an "Emily Rose" on you. But i applaud your inquisitive nature. At the risk of sounding like a mother(which i am) just be careful.