Pact Magic

Stepping aside from the obvious political tint of this blog, I wanted to pose a question to other people who might be familiar with the fantasy genre: What is the best internal system for magic in a urban setting? In other words, how does a system of magic operate given that the author is trying to follow magic realism. I have been thinking about this question for a while and the best and most simple system I can think of that provide an answer to readers but does not inundate them with a complicated system of magic that has the potential to be filled with contradictory loopholes if pact magic.

What is pact magic? Pact magic is when a human being gains superhuman powers through a pact with a higher being or a magical entity. In my story that I am currently writing, Clandestine Advent, the users of magic enter into a pact with an unknown entity force that enables them to use a limited amount of superhuman powers. In exchange for this power, the pact-holder must pay a "fee" or restitution for the powers used. This restitution is always different for ever pact-holder and can range from a loss of emotions to the need to cannibalize after each time the power is used. In terms of magic realism, it doesn't make much sense, but it at least is an internal system of logic that given certain inevitable suspensions of belief, is still logically feasible. I think...