If they are following the iOS then go to this website. http://injusticegodsamongus.wikia.com/wiki/Injustice:_Gods_Among_Us_iOS
Next one will be Red Son Deathstroke. Red Son Speed: Deathstroke and his teammates gain 5% Speed for each Red Son character on his team.
Supposedly his level two special is crazy strong, like level 3 damage strong. I might build a second RS team out of him and Grundy (since Deathstroke has low health). --- Well they tell you: never hit a man with a closed fist. But it is, on occasion, hilarious.