Floating in Relic
From Halopedia, the Halo wiki
The Floating in Relic glitch is a collision-related phenomenon present in the Halo 2 multiplayer map Relic. The error allows players to float in the air.
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 air approximately one Spartan/Elite high and will fall if you move, are moved, or die.
