Mongoose glitch
From Halopedia, the Halo wiki
In Forge Mode on any level grab a Mongoose and take it close to a barrier. Have someone get on and then a second person get on passenger. Have the driver get off but the passenger stay on. Have another person go into Forge mode, pick up the mongoose, and by using RT and the left stick push the Mongoose outside of the map. The passenger can then get off and he will be outside of the map.
