Serissa

 was a priestess of The Scaled Tyrant and leader of the Cult of the Caustic Heart.

Calanna said that Serissa was motherly and kind to her, encouraging the cult to treat her as special. She was able to convince her it was the way of the world to kill people - merchants and other innocents - in the Scaled Tyrant's name. Calianna came to realise Serissa and the cult were evil and ran away from them.