"Horde" is a new cooperative multiplayer mode in
Gears of War 2. In Horde mode, up to five players can work together to fight off "wave after wave" of alien foes, according to
Cliff Bleszinski of Epic.
[Joystiq: Engadget & Joystiq...Microsoft's E3 2008 keynote (July 14, 2008)] Players are given a short span of time between each encounter to regroup, and each successive wave of enemies becomes progressively more vicious.
[GameSpot: E3 2008: Gears of War 2 Update - Co-Op Info (July 14, 2008)] Horde Mode will allow up to 5 players to play together, as well as the multiple difficulty levels present in
Gears of War 2's campaign mode like Casual, Insane and Hardcore. There will be a singleplayer option in Horde Mode.