Solid Patch of Air
From Halopedia, the Halo wiki
On Ascension, have one person (Person A) get the Banshee and leave it sitting where it spawned. The other person (Person B) should grab the overshield and then stand at the Banshee's spawn point. If Person A boosts at just the right time when Person B jumps, then Person B will be knocked off of the ledge, through some clouds, and onto a solid patch of air outside of the level. Person B's only means of returning from that point would be to die and respawn.