In an interview with "There have been a number of rumours circulating about a multiplayer mode in Batman: Arkham City so let me start by saying, once and for all, that Batman: Arkham City is a 'single-player only' experience. Our thought process behind this was fairly simple: when we investigated adding multiplayer we asked, 'If we use all of the energy that is required to create multiplayer and instead focus this on the single player, would that deliver a better overall game?', Rocksteady studio director Sefton Hill stated,
"With the game now coming to the final stages, I can honestly say it would not have been possible to deliver Arkham City the way we wanted to if we'd have added multiplayer. So it might not be the fashionable choice, it might not get us an extra tick on the box, but we are convinced, and we hope that gamers will agree when they get to play the finished game, that we have made the right decision."
Let us know if you're disappointed or not with the lack of multiplayer or co-op.