Phantom glitch on The Arbiter
From Halopedia, the Halo wiki
When you start out on the level The Arbiter turn around and zoom in on the Phantoms. Then watch them, and shortly after they disappear into the clouds they will spin out of control crashing into a platform below. Sometimes they will even before hitting the platform stop in mid-air after falling quite a distance.
Also at the start of the video for that level, the Covenant Starships seem to be in the foreground (I.e. when the Phantoms go past the starships the Phantom appears to be behind them). You need to look closely but you can see it.
Also a little side-note, turn on subtitles, and read them as the Spec-Ops Leader gives his troops the battle speech. You will find a bit where Bungie haven't quite paid attention to the dialogue and the subtitles. Just look and find out.
