A career Supervillain on death row is taken to an alternate reality to defeat his invincible brother and become something he’s never been before: A Superhero.

*supervillan anyways. i'm guessing the government or powerful group controls the ability to change realities, but the stakes have to be high enough to make him want to defeat his brother instead of saying "ok i'll do it" and then flip flop since his brother is invincible to them to begin with.

don't need the word career since that's given with Supervillain (he's not your ordinary villain after all). Be careful with alternate realities. if he can just go back and forth, or even just once, what's so serious about being on death row? What would stop him from joining his invincible brother in the alternate reality if he clearly prefers being a superhero anyways?