Bilebound Ur'zul

Coming in Patch 12.1.

This demonic amalgamation was the result of a warlock's experiments in curse-infused alchemy. Whether the experiment was a success or failure depends on who you ask.

Riding Requirements:

Level 10
Apprentice Riding (ground)
Expert Riding (flying)

Source:

The Trading Post (seasonal)

Notes:

This horrifying green Ur'zul will be available from the Trading Post in an upcoming month. Unfortunately we can't say exactly when, as Blizzard don't announce Trading Post offerings ahead of time.