This mode is unlocked by finding the Reach for the Sky Achievment. It makes ALL dead bodies float, as if in low gravity on the moon. Very useful if you know how to make the bodies into a temporary meat shield but is mainly for decoration. It is not known if dead bodies have ever floated out of the map before.
Even though this does not affect earning of credits, it still can provide a meat shield sometimes if you are lucky. Also, getting the kill bonus, "corpslosion" is easier with moon corpse mode as grenades will stick to the bodies. However, the bodies can suddenly drift in the way when you're firing an explosive and kill yourself. Some players have even found the "lol cat" secret because of it because their dead corpse floated onto the "iceberg" in Frostbite. The corpses can be tossed into the enemies if they have explosives. With a bit of luck, they'll kill themselves from the corpses. Some people even try use moon corpses to kill themselves with an explosive, and try help their teammates by providing a shield or try drift out of the map!