The mode is called Flood and will support 10 players. The gameplay is similar to the Infection mode from previous Halo titles. Two players will start off as infected and their job will be to spread the disease to other players.
The developers also took this opportunity to reveal two new UNSC vehicles. First is a armored carrier called Mammoth. The second vehicle is a Mech that comes equipped with rocket launchers and twin cannons.
Halo 4 will be released exclusively for the Xbox 360 on November 6.