Since the days of World at War, Call of Duty has always had some kind of third game mode. In Treyarch's games, this third mode tends to be the beloved Zombies mode, and in Infinity Ward's lineup, this mode is often a variation on the Spec Ops challenges that were introduced with Call of Duty: Modern Warfare 2. Even the more disappointing Call of Duty entries have had an additional game mode, like Ghosts' Extinction mode, and Advanced Warfare's Exo Survival mode.