Once a Highborne, Xavius was the councilor to Queen Azshara, Empress of Nazjatar and the Naga. He was later transformed into the first satyr by Sargeras, and became the Nightmare Lord as a powerful sorcerer to the Old Gods.

Toward the end of WoW Legion, he took on the power of the Emerald Nightmare to turn himself into this.

Does not have a decay animation.

Credits to Blizzard.