I realize that this is more a group than it is a single character, but they deserve some video game love. You could have almost any roster. With that, it could bring back the style of the great PS2-era games X-Men Legends and X-Men Legends 2. Give me some online and couch co-op and let me play as Beast Boy, changing from a shark solving a puzzle to a gorilla smashing some baddies.
You could also have an unlock system where you have to help other members with missions before they become a playable character. Think of all the DLC you could have.