The Muse is a ghostly looking Draik who over the course of many years guided explorers to discover the Ruins of Elderus. He was also seemingly known by the ancient Vandagyres that built the ruins in the first place.
The Muse is capable of possessing Orion and controlling his actions and words. He did this to eventually lead Orion to clues surrounding his identity for unknown purposes, and well as to try and make Illusen and Jhudora reconcile.
He eventually possessed Orion again to help defeat Vocivus and solve the Grey Curse, claiming to have known Vocivus for a long time.