Heilong

Heilong is a Demon under the control of Lucy Yang and is kin to the Emperor of Nothingness, Armumahel.

Overview
Heilong appears as a titanic black dragon, dwarfing even the already giant Muspell with multiple fish-like fins along the length of its body, horns growing from its snout, brows and crown and surrounded by billowing plumes of black smoke.

It is summoned with a chant and the burning of a talisman by Lucy Yang:

"I beseech thee Black Emperor, Black Dragon and General of the North to eliminate this evil. Come forth Heilong! Urgent is our need. Sacred treasure and sign of destiny spread your black fog as I command!"

Powers and Abilities
Black Fog: Heilong can unleash a torrent of black fog from its mouth that cause demons that aren't high-level to become confused and attack one another. This fog is seemingly composed of Black Flames, but has been adjusted to such a level where it will not harm humans.

Trivia

 * Heilong is one of the Dragon Kings of the Four Seas of Chinese myth representing the North and season of Winter.