The mode isn't direct head-to-head combat. Instead, it extends the game's existing three-on-three fights to two people. Players set up their unit of heroes and villains, and then pit their squad against the AI of a team another player has put together. Battles provide players with Multiplayer Points, which determine one's place on the game's leaderboard.
At the end of each week, players receive tiered rewards based on their leaderboard rank. Those rewards include gear that can be used to upgrade characters' statistics and performance. In addition, players will be able to watch replays of their matches to get ideas on how to improve their team's lineup. Also included in the multiplayer update are new Gold Characters, increased promotion and level caps, bonus missions and a new Challenge Character Booster Pack.
Injustice: Gods Among Us debuted on iOS a year ago this month; the Android port, which was developed by Virtuous, launched last November. The multiplayer update is available on iOS today, and is coming to Android next month. You can check out a trailer for it above.