Beginning at 12:01 AM PST on October 31 and ending 27 hours later, Bungie will present the ranked Infection mode as one of Halo 3's many online playlists. The mode starts out with one player as a zombie, and more are added to the undead legion as the zombie takes down other players.

A few different brain-munching variants will be available, including Save One Bullet, which has limited ammunition, Creeping Death, where zombies are invisible, and Creeping Rockets, where humans get better armament but face off against tougher foes. The maps of the new playlist are said to be slightly modified for defense against the undead, with Bungie promising this is not the last of the its seasonal multiplayer offerings.