Floating in Relic
From Halopedia, the Halo wiki
The Floating in Relic Glitch can be done with either an Elite or a Spartan on the Halo 2 multiplayer map, Relic. Simply head to the ramps near the underground teleporter, nearest the beach. Get on the rails and jump repeatedly while looking left to right. On about the tenth try (maybe on the first try, maybe never, usually about tenth), you will land on nothing approximately one Spartan/Elite high and will fall if you: move, are moved or die. You may stay in the air because of lag so the game might think you are standing on another Spartan/Elite. You can do this by yourself (one console).