Mission: Osiris, Heroic difficulty, can be done solo
Near the end of the level you will see a group of Covenant troops fighting Prometheans. You need to help Elite General (golden armor) reach the entrance at the top of the hill. Pick up the best weapons before you leave cave (Light Rifle), stay on the right side of the map so you can see the entire battle field, don't get too close to him (he will start shooting at you) and don't let him die. You can send your Spartans forward so they will focus on the Promethean soldiers. If Elite dies, reload checkpoint asap.You can make a copy of your checkpoint using one of three available slots in menu so you don't have to restart entire level if you screw up.