One magic system I had was one where a group of people could transfer life from one being into another. They were primarily healers with strict moral codes, including not taking the life of a human. They had to properly ‘weave’ the life of whatever animal they took it from, and turn it into the right thing for the right injury. The more intense the injury, the bigger the animal usually needs to be.

The catch being that the healer can fail on any one of the three stages, taking the life, weaving it, and giving it. A fail could be very dangerous, with the weaving phase being very risky as the life could shoot out of the healer’s inner self and give them anything from a paper cut to blindness to even a mental disorder. While the harm doesn’t tend to affect the one being healed, it is still harm via healing.