this does not show up at all. tried a few times solo on heroic and mythic. it does not show up. KILL all bosses - port back to third boss area - nothing. is this something that will ever be fixed?
UPDATE: after a reset (my system) - it’s working now.
It is supposed to be 100%. if you beat it on heroic or mythic (must be solo and you cannot be in a group anywhere apparently) - you go back to third boss (portal) and it’s in the water to the left. you just need to pet it.