Kill your first skeleton.

Kill 100 enemies.

Kill 500 enemies.

Kill 100 enemies without dying.

Reach wave 10.

Land 50 headshots.

Kill 10 enemies within 10 seconds.

Use every weapon at least once.

Kill 100 enemies with the assault rifle.

Kill 50 enemies with the shotgun.

Kill 5 enemies with a single rocket.

Kill 25 enemies with your fists or grapple punch.

Score 50 dismemberment kills.

Kill 2 enemies with a single shot.

Unlock every other achievement.