So here's a thing. I'm thinking of apping a guy from a series with multiple magic systems. One of them he can and does use throughout canon. Another one he, like anyone else on the planet, theoretically could use. And indeed, at the end of canon he has a perfect knowledge of what can be done with it and how. Thing is, he doesn't like Magic System 2, and explicitly says he'd prefer to know much less about it than he does. Should I include an explanation thereof (insofar as such is available; there are, in theory, well over 10⁶⁰⁰ - a million googols - possible effects, of which maybe half a dozen are revealed to the reader) in the abilities section, or just mention it, or what?

Also he kinda literally turns into a god at the end, which is one reason I'm keeping this question post so vague. How would you guys prefer that kind of thing be handled?