Sledgehammer Games added character persistence to Call of Duty: Advanced Warfare's Exo Survivor mode because of the feedback to the survivor mode in Modern Warfare 3.
Advanced Warfare's co-op is a separate wave-based mode for up to four players. You start by picking from three Exo tiers, or classes of soldier: light, heavy or specialist. Then your team faces off against enemy types that include cloaked Exo soldiers, dogs, drones and mechs in increasingly difficult rounds, with random objectives thrown in to add variety.
It's similar to the survivor mode from Modern Warfare 3 in many ways, but differs in that your progression is retained during the course of a session. In Exo Survivor, when you wipe the game is over and you must start again from round one, but your character retains unlocked abilities.
"Because of the persistence we know people will enjoy it a lot more," Sledgehammer Games co-founder Glen Schofield told Eurogamer at EGX today.
"One of the things we heard on the last game was, when you died you have to start all over again. We found people really like to invest in their character. This one is about investing in a character, investing in your team and working your way through the different waves in different levels on different maps."
During Exo Survival you gain Upgrade Points, which are spent at Upgrade Stations dotted around the map. You can upgrade everything from your armour to your Exo abilities, your weapon type to your score streaks.
Exo Survival is designed to go on forever. "It's unlimited," Schofield said. "You just keep going, wave after wave after wave."
Indeed Sledgehammer has no idea how far players will get, but teams could last longer than they did with Modern Warfare 3. On Modern Warfare 3 the developers were stuck at round 30 for some time. With Advanced Warfare test has already reached round 70 - and that's down to the persistence.
"60 or 70 is the highest number we've had," Schofield said. "The thing is, you're also upgrading more and more. So we don't know where it ends.
"Because the enemies are different, because you're working four-player co-op, because the armoury system is so much more customisable, we have no idea what the highest people will get."
Adding a dash of variety are rounds that include additional assignments, such as collect dog tags or diffuse EMP bombs. If you complete these assignments you earn bonus upgrade points. But if you fail to complete them before the round is over, the next round will be extra hard.
"You'll be like, well, I don't know if I want to take that challenge," Schofield said. "But the game is telling you you better take that challenge or something might get harder. So you have all these little side things where you might earn something more, but you may lose something if you don't do it."