Rocksteady will release a free Batman: Arkham City tomorrow on Xbox Live to thank fans for their loyalty. See, even Gotham celebrates Christmas.
The "Batman Incorporated" costume is similar to Batman's default garb, but made from heavier-looking fabrics and with a more pronounced Bat symbol on the chest. There have been crazier makeovers, but hey - it's free.
And you won't need to play the whole game through to unlock it, or indeed any other optional Batgear. Simply apply the following combination of D-pad inputs to the main menu screen, after you choose your save device:
Left, Left, Down, Down, Left, Left, Right, Up, Up, Down
An audio cue will play if the code has worked and you'll be given a choice of alternative costumes. Cheats are brilliant, aren't they. More of this sort of thing, developers.