There is a new Marvel game for mobile devices that was just released called Marvel Future Fight. It is similar to MUA where you have a team of Heroes that you level up and play with. The starters after the tutorial are Black Widow and Iron Man and you get Captain America after a mission or two. You do have to work at getting more characters, but there is a free draw every 24 hours that can give you heroes. My only complaint is a lack of X-Men in the roster, but it looks like there will be updates every now and then as Rocket, Groot, Star-Lord, and Drax all appear on a loading screen, but aren't playable yet.