Disappearing Truth
From Halopedia, the Halo wiki
The Disappearing Truth is a glitch that can be performed on Halo 3 level The covenant.
How to do it
In the last section of the level The covenant, after you have reached and killed the Prophet of Truth and after you have being attacked by the Flood, you can melee or teabag the Prophet of Truth a couple of times, causing him to fall through the platform on which his body rests. When he falls beneath the platform you can see him, but sadly you cannot reach him.
This also works on flood combat forms.
