Looks like we're going multiplayer in Batman: Arkham City
as confirmed by Rocksteady
in the new PSM magazine. Other then Rocksteady mentioning that it'll be possible, the details are pretty scarce.
I'd love to be able to patrol the streets and finish quests with another person or two if there's a co-op mode. I don't know who would want to be Robin though but I'd definitely take part as Nightwing. I'm guessing there would be some deathmatch mode in there as I can easily see that put into the game.
Can't wait to check it out and I hope we hear more about this soon.