This mode is where the players ban together to fight wave after wave of enemies (they could be these unplayable characters like zombies) and each wave gets harder and harder! it could even have the option to set it from co-op to verses where all 4 (or 2 players against 2, and 1 against 1) player try to see how many enemies they can kill before they are overwhelmed and die, the one with the most kills being the winner. When a zombie hits you x amount of times (you can set it) you die, and obviously you kill them by building up meter to perform a super! I feel like this will make a really great Team oriented game mode since when playing are playing the co-op mode of this, all 4 of them can really work together to take out the wave of enemies plus this mode keeps going until all players are dead (you can set it to if 1 dies, its game over, or of 1 dies, it keeps going till you all die) plus there can be leaderboards for best score and how long you survived and stuff.
So what do you think?