My theory is simple:
My first thought was that you could boost a natural human attribute but I was later informed that to do so would alter the persons health. But as it stands it was never a matter as the person being a person, mearley that the body provide a vessel so that a person may become a weapon... So you don't care if this person looses control of the magic, its no longer about him/her. You instead withdraw the persons soul and replace it with a spell-lets say a spell that causes death. Then as you could bring to life a demon or angel, you use your magic to bring this thing now a body for the spell to life. And whatever it touches is effected by the spell inhabiting its body. In this case-ultimately creating a "Grim Reaper" from someones body, whom is now a biological elemental rather then a human being.
However, the second part of this theory is weather or not one can place certain traits into an object, for example, a stone, that once touched could absorb a persons soul.
I understand that this boarders on fluffy but whoever reads this just pretend for a moment it is possible, how would one go about such a concept?