Players can choose from four different classes of Exo, which grant different abilities and score-streaks. Weapons and score-streaks can be upgraded throughout each match. After a certain number of rounds, players are given objectives to perform, such as defending a location, or collecting intel from fallen enemies. Completing the objectives grant players bonus upgrade points; not completing them result in the players being punished, such as having their Exo suits temporarily disabled or activating hostile security turrets. Exo Survival is played on the game's multiplayer maps, with a total of 13 maps divived into four tiers. Each tier can be unlocked by playing the previous tier and survive a specific number of rounds. Exo Zombies was first teased at the end of the Exo Survival map "Riot", and was officially announced with the "Havoc" downloadable content (DLC) pack. The game features zombies that utilize exo suits, giving them more maneuverability. The game mode stars five brand new characters. Exo Zombies plays similarly to the original Zombies game mode that has been featured in Treyarch's "Call of Duty" games since "": up to four players must survive against endless waves of undead enemies, with an optional story quest that can be completed at any time during a match. Players earn points by injuring and/or killing zombies, and use those points to open doors/clear obstacles, or buy new weapons and perks to strengthen their chance of survival. Players can also acquire exo suits in the game mode, allowing them to utilize new movements. Different types of zombies are present in the game, including Charger zombies that have increased movement speed, and Electro-magnetic zombies (EMZs) that can disable the players' Exo suit in close proximity. The first Exo Zombies map, "Outbreak", was released as part of the "Havoc" DLC map pack. The second map, "Infection", was released as part of the "Ascendance" DLC pack. The third map, "Carrier", was released as part of the "Supremacy" DLC pack. The final map, "Descent", was released as part of the "Reckoning" DLC pack. In 2054, U.S. Marines Private Jackson "Jack" Mitchell (Troy Baker) and Private William "Will" Irons (Paul Telfer) take part in an operation to repel a North Korean invasion of Seoul, under the command of Sergeant Cormack (Russell Richardson). During the firefight, Will is killed and Mitchell loses his arm, resulting in him being discharged from military service.