Use a large medkit to heal an injury of 5% or less.

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

Set 10 zombies on fire simultaneously.

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

Loot 5 Exceptional Weapons.

Complete act IV.

Kill 10 zombies in a row with headshots.

Find 120 collectibles.

Heal yourself with a medkit 100 times.

Complete act II.

Kill 5 Infected in a row with a single blow.

Kill 50 human enemies.

Reach level 25.