There are two missions you can use that I know of.
First (easiest, imo): The one where you start out in the falcon with the mounted machine gun. Just keep shooting down banshees. Turn on all skulls except black eye... I think...
Watch out for the shade turrets. They'll rip you to shreds really quick. If your falcon's on fire, land somewhere and press down on the d-pad to get another one.Took me a little under 2 hours doing it this way, I think?
Second: The one where you get to operate the mass driver cannon at the end of the stage. All you have to do is grenade bounce and use the concussion rifle to access the mass driver before the final part of the level is initiated. This is harder for a few reasons...
-If you do it on Legendary with skulls on for more points, you have to go through enemies.
-If you're not too great with grenade bounces/concussion rifle jumping, you'll probably kill yourself.
-It's a lot slower than the first method.
Took me a lot longer than two hours. Don't remember exactly how long.
Sorry, this isn't really helpful anymore since the weekly challenge expired, but... you'll know what to do next time it rolls around.
This post was edited by iamluke21393 on Apr 2 2012 10:30pm