The Mystic Path was a cartel of traders and noblemen hailing from the planet Maginor, the capital of the Niaides sub-sector, Viceroy sector, in Ultima Segmentum. They utilized Warp artifacts to increase demand for their goods, a practice that slowly and surely corrupted them.
Almost two centuries before his demise, Inquisitor Quixos encountered the Mystic Path. Rather than destroy them, as any other Inquisitor would have done, Quixos instead built up a relationship with them, so much so that they eventually became the personal cult of the Chaos-corrupted Inquisitor. The Path eventually spread throughout Ultima Segmentum and beyond, with Quixos as their patron.
Two Inquisitors - Helgrund first, and then Hetris Lugenbrau in 239.M41 - arrived on Maginor and battled the Mystic Path, eventually coming into conflict with Quixos himself. Both times, however, the loyal Inquisitors were killed when the daemonblade wielded by Quixos caused them to immolate.
The Mystic Path's last known activities with Quixos took place around the time of Quixos' eventual death on Farness Beta, in 343.M41. Aided by cultists of the Path, Quixos was attempting to duplicate the pylons of Cadia in an effort to collapse the Eye of Terror in on itself. Before he could complete this plan, however, Quixos was killed in single combat with Inquisitor Gregor Eisenhorn. The fate of the Mystic Path after this is unknown, but it is speculated that they were purged from Maginor by the Ordos Niaides shortly after Quixos' death.