God Mode

Just a slight explanation for this achievement. If you plan to do this for co-op, you must have no one die through the whole map or it won't count. I've gone through countless times of not dying myself but still completing the map but because my teammates had died then the achievement didn't pop. I suggest getting a group of people you know together to do this and go on bronze and vote hades moon which seems to be the easiest to do this on to unlock your achievement. Again this is just a greater explanation on this achievement and means "you" if you're playing solo but means "you and your team" if playing with a group.

EDIT: My achievement just popped and I was playing with 2 other people and 1 of them died once. It seems like this achievement is glitched as I have gone a few games without dying (including the one I finally got the achievement to pop on).

EDIT 2: As Antagonistic stated, clearing your system cache might help with obtaining this achievement. To do a system cache, on your xbox 360 dashboard go to settings-> system -> storage -> hit Y on the hard drive and clear system cache. Then reboot the game, you may have to update and then play the game as usual and see if the achievement pops.