This guy was one of the 3 "crocolisks" that spawn if you have the "A Cleansing Song" daily quest from Sholazar Basin.
These "crocolisks" consist of a slime, a ghost hydra, and a ghost crocolisk(this guy).
All of these were tameable during the launch of Wrath of the Lich King, but only for like 2-3 months in which Blizzard make them all untameable.
Now it makes sense on why they did this, seeing that a slime and hydra (at the time) were not considered tameable beasts let alone a crocolisk.
However, it did not make sense to me on why Ha-Khalan was also made untameable in the fact that it is a crocolisk.
Sure you may argue it having a ghost-like appearance could of made it untameable, (Which at the time, weren't that many of them) but Blizzard didn't seem to care when hunters were able to tame Ghost Saber or the Ghost Worm. Especially, when in Cata and MoP they started to add new ghost pets for hunters to tame. So why not this guy?
It doesn't makes sense on why it wasn't reverted back to a tameable beast. Crocolisk need some love man.

Then came WoD were they finally made hydras tameable as well as the Ghost Hydra. But still poor O'Khalan still untameable.
What I'm trying to say is "I think it's time to make Ha-Khalan tameable again."
And I need the help of the Hunter Community to send a message to Blizzard that should of been fixed a long time ago.