Lanticore Spawnling

Source
Lanticore Spawnling is a guaranteed drop from The Lanticore, a rare elite that has a chance to spawn in Upper Blackrock Spire on Heroic mode. Note that it is no longer guaranteed per-person if the loot system is set to Personal Loot.

Pet Journal
No one knows what deep part of Blackwing Descent the Lanticore was kept in, but it probably smelled pretty awful.