[quote=@Ellri]
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.
[/quote]Interesting idea for a power, but how much control would the player have over it? Is it an activated power, where they can choose to corrode something when they touch it but can equally choose not to, or a permanently active power, where anything they touch, at any time, would corrode?

[quote=@Ellri]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.[/quote]There's already enough source material around to easily accommodate things like super-strength, melting cyromancers and the like, so I'm not having too much trouble building gameplay models for how to deal with their powers. It's the unusual and esoteric abilities which cause problems, since they can be used in unexpected ways which break the game rules too easily.

[quote=@Ellri]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.[/quote]Nice idea, but with characters like Reed 'Mr Fantastic' Richards, Elongated Man and Plastic Man around there's enough source material for those powers as well. :)