written into a corner

I read an interesting article tonight on the use and types of magic in fantasy novels. The problem i'm facing is that in my book I started out to create a superhero of sorts. The problem is that now I've done it and I don't know what to do with him. He's too powerful. Can too easily fix problems. I have to go back and put some checks on that. I need a way to balance out the good with some bad.

Now I've got some work cut out for me: I need to create some rules which govern the use of magic in my world. I need to find my hero's kryptonite!