When we spoke to Double Fine Productions' Tim Schafer at E3, he teased the reveal of Brütal Legend's then unannounced multiplayer modes. Consider (one of) those multiplayer modes a secret no more, thanks to the ancient tomes of Xbox.com!!
The game's product page describes the "four-versus-four 'skirmish' multiplayer" mode as a holy union of "action combat with a strategic unit-control mechanic." We know that Brütal Legend protagonist Eddie Riggs can amass armies of headbangers, groupies and amp-wielding roadies to do battle in the game's single player mode, but it appears we'll be able to take that action-strategery on the internets.
See? "As the leader of one of the factions in the game, direct your armies in a Battle of the Bands where the trophy is survival, and even take your battle online over Xbox LIVE." Seems pretty clear to us.