Dubbed "Mad Moxxi's Underdome Riot," the follow-up to "Zombie Island" brings three new "Riot Mode" areas to the shooter-RPG, where players can face off against an "onslaught of Pandora's baddest enemies," along with more storage capacity via a new "bank feature" and the ability to earn two more skill points through quest rewards.

Coming to all three versions, the 800 Microsoft Points / $10 download hits Xbox 360 on December 29, PlayStation 3 on January 7, then PC at some unknown point.

Update: Gearbox has clarified that the "Riot Mode" arenas "are not just new deathmatch areas," but "an entirely new game mode" in which players face off against waves of enemies a la Gears of War 2's Horde Mode or Halo 3: ODST's Firefight.