Injustice: Gods Among Us won't actually be out until April 16, but the iOS companion app is totally available already. Yes, there's a companion app for the upcoming DC fighter, and it's apparently pretty good.
Okay, so it's probably not as complete as the final game, but this should tide you over until then, assuming you've got an iPhone or iPad. As of writing, this app's been rated 1,770 times on the Apple Store, with five stars. That's gotta mean something, right?
The game does look pretty good though, and features 3v3 fights, plus a fairly complete roster. What is it? Apparently a fighter meets collectible card game. Cross-platform functionality is, of course, a thing, and you can unlock items for the console versions using the mobile one, and vice versa.
The app is free, so no real loss if you don't end up digging it.