Save 5 people besieged by zombies.

Complete 25 quests while playing with at least one co-op partner.

Kill 50 human enemies.

Complete 5 quests with 3 co-op partners.

Play with 10 different co-op partners for at least 15 minutes each.

Sever 100 limbs.

Complete 5 quests in a single co-op game with the same partners.

Travel a distance of 20 kilometers on foot.

Play in a co-op team of 4 different playable characters.

Reach level 10.

Join another player's game.

Defeat ten enemies with propane or acetylene tank explosions