Knife an enemy without him ever knowing you were there in Single Player or Special Ops.

Escape from C-Block

Kill two enemies with one throw of the Battle Disc

Wipe out all of the Marines in the Colony

Liberate the Matriarch

Find a way through Gateway

Kill 20 minions.

Release Jennings from his Trap.

Kill 10 minions.

First kill with a Table Leg.

Release Amanda from her Trap.

Used Health Syringe for the first time.

Unlocked first door.