A new mysterious villain appeared who's only goal is it to entertain himself. He's really powerful and can control reality. One day he decided to teleport the Justíce League and the Avengers into a battle arena to see who's the stronger superhero team

The villain floats about the two hero teams

Villain: "now fight... The loser team dies and the winner can keep their universe. And if you both don't fight them all of you die and so does your universe and everyone you love~"

(On what team are you on? Powers, name etc)