Most of the virtual items in the OASIS were created by the system at random, and they would "drop" when you killed an NPC or completed a quest. The rarest such items were artifacts, superpowerful magic items that gave their owners incredible abilities. Only a few hundred of these artifacts existed, and most of them dated back to the earliest days of the OASIS, when it was still primarily an MMO game. Every artifact was unique, meaning that only one copy of it existed in the entire simulation. Usually, the way to obtain an artifact was to defeat some godlike villain at the end of a high-level quest. If you got lucky, the bad guy would drop an artifact when you killed him. You could also obtain an artifact by killing an avatar who had one in its inventory, or by purchasing one in an online auction.