He is "The ultimate raid boss". He raids you of all your precious engrams; and gives you the dregs from Xurs barrel of loot. He hands over his ill gotten booty to Xur for a slice of the profits, after you buy from Xur. However, the Cryptarch makes the occasional blunder when he is over worked by a horde of guardians. As such, that lucky guardian quickly vanishes, so as not to draw attention to the blunder or loose favour with other guardians. BTW: His "Master" degree came from Acme school for the slight of hand. Who's headmasters are: Xur, Atheon, Eris, Crota

hed give shitty loot no doubt