Phantom glitch on The Arbiter
From Halopedia, the Halo wiki
As soon as you start the level, turn around and zoom in on the Phantoms. After watching them for awhile, they disappear into the clouds and spin out of control. One Phantom could crash onto a platform below. The other two will keep on falling until they hit the bottom of the level. A logical explanation as to why this happens may be because Bungie only planned for them to travel a certain distance, and upon reaching the end of their route, the game physics take over.
- Sometimes, when spinning, an Elite will fly out, and then disappear in barely a second.