you could always have a villain like "Captain Corrosion"... Rather than the classic control over metal, he's very good at corroding stuff, at breaking down metal. Perfect for those pesky vault doors and guard weapons.

A good superpower should also have disadvantages, or at least inconveniences. Super-strength, for example, can be limited by the fact that finer motor control on fragile things like non-solid metal objects tend to break when squeezed.

A cryomancer probably won't do too well in hot environments, and visa versa for the pyromancer and cold environments.

another interesting superpower would be someone capable of literally flattening themselves against a wall. And so forth. There's simply no real limit to what can be done.