When the level starts out either get in the warthog or the scorpian tank. Kill everyone on the brigde or drive past them until u get to the end of the bridge. Once your at the end kill your marines. Prepare to enter the tunnel but dont go in. kill all the ghosts and wraiths. Before entering the tunnel the lady or w/e her name is will say something about a welcome party. 4 banshees will come and kill them all. Then 2 more will come and ONLY kill 1! Use your battle riffle to shoot and the banshees wings but do not kill it. Start walking in the tunnel while still facing the banshee. He will go in the tunnel with you and fly back out. Even though he flys bak out walk a bit deeper in the tunnel and stop. he will come and back fly back out. Move back again and stop. On the 3rd time of doin that, he will not fly out of the tunel. Keep walking forward and he will still be following you. Up ahead there are some marines in a warthog. kill them. Make sure the banshee is still following you. Up ahead there are jackals on that bridgy thing. Kill them and walk to the middle of the bridge. Turn around and make sure the banshee is coming at you and jump or walk down on the other side with all the aliens. The banshee will follow but make sure you kill all the alines. Keep walking deeper and their is another bridge thingy. walk on the middle of that and face the banshee. If the banshee ever gets stuck in a corner, Walk right beside it and start walking backwards he will be unstuck. Get him over that 2nd roadblock/bridge thingy and walk in the entrance of the red room. stand thier and start shooting but not at the banshee. Start to walk backwards slowly and he will folow u in that room. Go forward and go to the LEFT tunnel and stand in the entrance on that tunnel. Walk back VERY VERY SlOWLY and he will follow u. When the screen says, "Loading-" press x quickly b4 the screen says "loading-done". Fly out of the tunnel and turn around and start flying up. U will c 2 bridge like things. Fly to the one thats closes to u. Fly the banshee on it and get out. There will b this orange cone on the bridge and floating in mid air is the scarab gun!!!ENJOY Ps: Dont shoot the scarab gun too close to you like at a wall or something.
i thought it was helpful