In Gears of War 2, the COG continues its fight against the Locust horde, who are attempting to sink all of the cities on the planet Sera. Sergeant Marcus Fenix leads Delta Squad into the depths of the planet to try to stop the Locust during the assault upon Locust territory. The player controls Fenix in the main mission campaign, with the ability to play cooperatively with a second player controlling Fenix's best friend and fellow Squad member Dominic "Dom" Santiago. The game includes several existing and new multiplayer modes including five-on-five battles between human and Locust forces, and a "Horde" mode that challenges up to five players against waves of Locust forces with ever-increasing strength. New weapons and gameplay mechanics such as "chainsaw duels" and the ability to use downed foes as "meatshields" were added to the game.