Free Play mode:Complete the game to play any Story mode live in Free Play mode.Achievements:ACHIEVEMENT – HOW TO UNLOCKThe Best of the Best (25 points) – Complete all single player levels 1-5 on Elite difficulty. Old Soldier (20 points) – Complete all single player levels 1-5. Co-op Campaigner (10 points) – Complete any multiplayer level. War of Attrition (20 points) – Kill 1000 aliens in single player. Vital Statistics (25 points) – Finish