Dendar, The Night Serpent

Dendar was a colossal serpent who spent her time devouring the nightmares and fears of both mortals and immortals in hopes of bringing about the end of the world. She was some 300 feet long with blue-black scales, yellow eyes, and a huge maw filled with four fangs, spittle, and the bones of some of her former victims.
Dendar was thought to have been created when the first mortal dream occurred, and she devoured the nightmares of the living ever since. Even the gods were not immune to her ravenous appetite for their dreams.
Cults to worship Dendar existed almost as long as she did. One of these cults was located in the ancient city of ________, in the jungles of Chult where those who worshiped her, often kidnapped victims and fed them poisons to cause them to dream.
The primary opposition to Dendar and her cults was lead by the followers of Ubtao, who thought Dendar lived in a mountain and would emerge one day to devour the sun. The followers of Ubtao saw it as their sacred duty to battle her.