Chernovog

Also known as the Green God, Chernovog is a demon prince mentioned in Expedition to Castle Ravenloft. He is served by the cult of Chernovog, which in the module in question consists of the Witches of Lysaga Hill led by Baba Zelenna. The witches hope to summon their master, and his aspect may appear if their plan is not foiled and the proper subplot is in place.

In the History of Barovia

Chernovog is said to have been conjured by an ancient order of witches at Lysaga Hill ages past but slain by the paladin Lugdana. Chernovog was sent back to the Abyss, but the cost of victory caused the loss of the paladin's life.