.IROTT is the third game of the series.
Battle mode: Where you and your opponent can fight
Free roam: You can travel around th entire DC universe.
After a year or so after Lex Luthor lost his money, he is still homeless in Gotham. He then meets the Joker and they decided to make the heroes pay for defeating them and make the Injustice league. Meanwhile, While Zatanna was trying to summon Batman, she summons a future incrnation instead along with many of is villains.