After the Wedding That Never Was, Strahd von Zarovich quelled the rebelling great houses that plagued his campaigns across Barovia. However, with noble families and towns dispatched, he heard of an unexpected gathering at Yester Hill; the hill-folk who occupied the area were looking to make a push against the Darklord. As followers of the Ladies Three, these primitive tribes made a last stand against a bulwark of Strahd's Undead forces. Led by the Blood Chief Kavan and the planar traveler Jaghr of the Longtooth, the fearsome Barbarians fought in the name of the Lady of the Mountain.
Martial might was not enough to stand against Strahd in his new incarnation, however. He invoked the magic of a Dark Power as his forces scattered the hill-folk. Kavan was lost in the growing mists around the hill, and was hunted and killed by Strahd's chamberlain Rahadin, though a small part of his spirit lingered in the Blood Spear he left behind. Jaghr, meanwhile, followed a Vistani prophecy and traveled north with as many hill-folk as he could; there, he established a religion unto his own, being named "Wolf-Father" and spreading Lycanthropy to Barovia.
The failed battle left the Lady of the Mountain without worshippers, and she recklessly attacked Strahd in physical form. The blood spilt from that battle coagulated around a lone tree that became a Gulthias Tree, which blossomed from the Archfey's corpse. It grew over her mountain fane, and Strahd hung the corpses and bones of the hill-tribes from the branches of the sprouting tree, an act that finally Desecrated the Lady's altar below. With her power tarnished, Strahd subsumed her powers over Barovia's wildlife without resistance.
He would later complete the Desecration Of The Swamp Fane and the Desecration Of The Forest Fane, gaining total control over shaping the landscape of Barovia. He would maintain this ability until the Slaying Of Strahd.