Iris, The Lady snake

Believed to be an evil titan, and worshiped by the northwest. Her followers would pay tribute by dissolve sacrifice in acid, and then drinking it. This would taint the worshipers, eventually turning them to the fearsome Yuan-ti. When Xul was banished by the hands of Naxolotl, Iris escaped underground, forming the caverns of the Underdark in Faran. It was her orders hat had gotten Naxolotl killed.