Use the following trick to get an unlimited Spartan laser on last level "Halo". Play through the level until you meet up with Sergeant Johnson. Shoot him until he falls down and drops the Spartan laser. Quickly pick it up and shoot it at him. Keep shooting him until he kills you. When you respawn, knock him down again and pick up his laser. He should get back up with another laser on his back. When he does, shoot him down again and pick up the new gun he drops. This laser should have unlimited Spartan ammunition. This makes it easier to destroy the Guilty Spark 343.