I say Jason Todd (voiced by jensen ackles from under the red hood because he did a great job) and hush as main villains. Go with ra's reviving Jason years earlier and batman interogating him about it (similar to under red hood movie). While hush is trying to pose Bruce. Maybe joker really is alive and it was clayface so Jason has someone besides batman to fight. Play as Jason in some of story mode and free roam. Robin vs robin action. Throw in a couple other fun villains, killer croc, fire fly, black mask, freeze, two-face, penguin, talia, ra's, jack Ryder as the creeper, deathstroke. Joe chill maybe. If there's scarecrow, I'd like batman to hallucinate about Jason like he did about his parents in the first one. Azreal will probably have a role. Maybe riddler solves Bruce's identity. Maybe a Gotham city sirens thing with catwoman poison ivy and Harley. Batmobile/batplane mission. Being able to go to The actual batcave and Wayne manor and be Bruce/Dick/Jason/Tim walking around in the manor. DLC based off red hood lost days maybe. Appearance at wayne enterprises by lucious fox. Either way, must have a good long story.