Kill an infected teammate with a headshot before they become a zombie in any mode.

Save every hostage

Kill 100 enemies with a sniper rifle

Complete the third mission of the U.S.S. campaign.

Complete the fourth mission of the U.S.S. campaign.

Infected 13 times (lifetime)

Use 15 enemies as human shields

Free teammate from Licker grapple.

Complete Chapter 5 on any difficulty level

Survive an entire level without needing to be revived on normal difficulty or above

Collect $1,000,000

Allow your partner to snipe 5 guys while in mock surrender

Co-op snipe 5 enemies