Vashna Acolytes are the wicked priests of the Darklord. After the defeat of Barraka, the Vassagonian renegade warlord, in MS 5054, it was common belief that the Brotherhood was destroyed forever. Actually some of them managed to escape and established in the city of Quarlen.
Years later, after the fall of the Darklords, Lone Wolf also meets some acolytes of Vashna in Mogaruith, where many agents of Naar were uniting in the common cause of annihilating all that's good on Magnamund.
Finally, LW destroys the cult in MS 5077 during its ultimate ceremony in the mountains around the Maakengorge, where they were trying to summon Vashna back from the dead. It is believed that the cult has disbanded after this event, but where these foul servants of Naar are concerned, nothing is certain.