A mode for 1-4 players. Each character starts off in respective spawning locations. After an interval of 15 seconds players get attacked by enemies from the universe of the for players. For example if you were playing as Dante, Big Daddy, Nariko and Kratos. You'd be attack by Demons, Soldiers, splicers and zombie Spartans.
During the first wave enemie die rather easily and as the levels progress enemies get more aggressive as it takes more to kill them.
Enemies also evolve from shambling enemies to enemies that run at you with the intent of ripping you apart. Stages will play apart in this as well. For example, if you're playing on Hades you'll see more of hades' undead Spartans. If you're playing on Columbia you'll see more splicers.
Next concerning the health bar, you can have a health bar beneath the super bar. By the way, supers kill things instantly. As the levels progress that changes.