Zombies ADD-ON

Darkness descends and the undead have risen! As legions of ravenous zombies seek to devour all in their path, players' reflexes, accuracy, and ingenuity will be put to the ultimate test in a fight for survival.  Battle through two new stages of increasing difficulty in an effort to quell the zombie hordes and emerge victorious.  Novice to experienced shooters alike can hone their skills as they undertake the challenge of withstanding the relentless zombie threat.
 
Zombies! ADD-ON Features:
- Two new maps (Warehouse and Laboratory)
- Two different game modes (Survival and Onslaught)
- New co-op gameplay
- Two new enemy types