Quote Originally Posted by OmegaZero_Alpha
or is multiplayer co-op against zombie NPCs?
The horde of regular zombies is controlled by the computer. There is no set amount of them, they just continue to spawn until you complete the objective. People playing the zombies can only be one of four classes and players can only play zombie bosses in Deathmatch mode.

Quote Originally Posted by Drunken_F00l
I wouldn't count on it.
I stand corrected