1. Start out on the level Metropolis, and I recomend doing this on easy because you will get shot a lot. (It also be wise to do this on co-op)
2. kill the marines and continue across the bridge. When you are at the middle of the bridge you will see 2 more allies, kill them both.
3. When you are across the bridge 2 banshees should apear above the tunnel. shoot one a little with the machine gun to lure it in to the tunnel.
4. Try to get the banshee to come down into the tunnel and if it goes back out then just shoot it again.
5. Once down in the tunnel where it is no longer going down hill if you look on your right you will see a warthog. Shoot it as many times as it takes to kill all of the marines in it.
6. You should arrive at a barrier with many covenant past it, you can either get out of the tank or drive it up the slope and continue in tank if you know how to get it to the other side.
7. Stay near the banshee at all times to make sure that it does not leave the tunnel.
8. It will get stuck in corners a lot and the best way to get it out is to go behind it and back up.
9. Once you have killed all of the covenant in the tunnel lead it in the smaller tunnel that you must continue through.
10. The way to lure it through the small circular part of the tunnel is to shoot off its wings.
11. As soon as you see Loading.... press X and if you did it right you should get in the banshee. If you did it to late you will have to start all over.
12. Once out of the tunnel fly go as fast as you can away because of the grunt on the turret and all of the jackals with beam rifles.
13. When you are out of that area look up and you should see two giant bridges. Go to the one nearest to you.
14. Once on the first bridge fly to the middle of it and you should see a orange cone with what looks like a plasma rifle hovering over it, it is accualy the scarab gun.
15. You can now fly down and finish the level or just play around with it.