The Hero is ultimately coerced into assisting Ad Avis' Dark Master in collecting the Dark Rituals that will allow Avoozl the Dark One (an obvious Cthulhu pastiche, and most likely a reference to the Slavic deity Chernobog) to manifest in Mordavia's world.
The hero is forced to assist Ad Avis' dark master in obtaining the necessary rituals for Avoozl, a being drawing inspiration from both Cthulhu and the Slavic deity Chernobog, to enter Mordavia.