Assault On The Control Room: Spinning Ring:

At the Halo start up screen, choose multiplayer mode. Choose cooperative play at the next screen, then choose your profiles at the next. Choose the level where in the beginning it says, "I would have been your daddy" (Assault On The Control Room). On the difficulty screen, choose legendary. When the level starts after the introduction sequence, have one of the players quickly press X when the "Press X to get on the Pelican" message appears. That player will re-board the ship and start flying with it down the hole. The other player will quickly die because of the aliens, and will be respawned on the spinning ring. Make sure to jump where there are gaps. If you are good enough, you can even jump to a nearby ledge. Additionally, once you are respawned on the ring, quickly jump off and fall to your death. Sometimes you will be respawned on the lowest ledge in all the blue haze, and a "Press X to flip the Pelican" will appear that the top of the screen very briefly.