Halo 3: ODST will hit retail shelves on September 22, but if you pre-order the game now from participating retailers, you’ll receive a token to unlock UNSC hero Sgt. Johnson as a playable character in the Firefight Mode.

Firefight is a cooperative multiplayer mode where you and your squad of fellow ODST’s will battle waves of Covenant enemies. As you progress, the onslaught of foes will become more challenging.

This mode essentially sounds like an ODST version of Horde from Gears of War 2 and should provide a decent amount of fun.