This mount comes from Silthide in Talador (Draenor). He is one of the 7 rare spawn mounts available in Draenor.
There is a 100% drop rate on this mount and everyone who tags him will receive one.
Silthide himself can be found at one of 5 spawn points – Cords 62.32 – 62.45 – 67.59 – 80.55 – 54.83. He has a spawn rate of around 12-28 hrs.
He is usually be surrounded by Riverwallowers so if you want to avoid being knocked back into more trouble I would clear the area a little.
Silthide himself is a level 100 elite and has around 2200k hp. The fight is very easy at 110 and is over in a few seconds.
I personally put out a call in general chat to see if there was anyone else camping or just in the vicinity that might like to nab the mount as well.