2K Games and Gearbox have announced the second DLC for Borderlands called "Madd Moxxi's Underdome Riot". This DLC will arrive December 29th for Xbox 360 for 800 MS Points, January 7th for Playstation 3 for $9.99, and at some future point for PC with a currently undisclosed price.

Mad Moxxi’s Underdome Riot is an intense single-player or cooperative experience that expands the mayhem by adding three new Riot Mode arenas where players will endure an onslaught of Pandora’s baddest enemies. Working together, players will fend off the masses as they fight for fame, honor, and more importantly, loot. Mad Moxxi’s Underdome Riot also adds a new bank feature, which allows players extra storage capacity for when they encounter one of the more than 16 million weapons that Borderlands has to offer; and the ability to acquire two additional skill points as quest rewards, making their characters even more powerful than before.

Full press release in the comments, as usual.

Update: Kotaku

from Gearbox Software stating that Undererdome Riot is "not just new deathmatch areas."

CEO Randy Pitchford notes "This is an ENTIRELY NEW GAME MODE."

"Think [Halo 3] ODST's 'Firefight' or Gears of War's 'Horde Mode.' Cash, prizes and competition!" Pitchford said in a statement from Gearbox. "It's like Smash TV in coop FPS, but in the Borderlands."

Gearbox reps say the new Borderlands downloadable content "expands greatly on the possibilities of combat as well adding a ton of new rules such as vampire mode or low gravity mode..."