As a fan of large and obnoxious mounts, I simply couldn't say no to this guy. The Sunhide Gronnling drops off a rare mob called Poundfist in Gorgrond. This isn't your ordinary rare. This one actually lives up to its name. Poundfist has a 48-96 hour respawn timer, and on top of that this timer is reset back to zero whenever the server is reset (including maintenance). This kept Poundfist from spawning at all until the 10th day of Warlords of Draenor. All of the unscheduled maintenance and rolling restarts kept him from ever appearing.
When he did start spawning about a week ago, people gathered by the hundreds at his spawn points. The one upside to Poundfist is that everyone who tags him will get the mount, regardless of group or faction. Unfortunately, he has 5 different spawn points. They are spread out enough that it's possible you'll miss him if he spawns at another one. He's only level 95 and his health doesn't scale up nearly enough to handle all of the people attacking him. On top of that, the phasing that was introduced to help server loads means that you could be in a different phase than the one he spawns in. Most frightening of all, these separate phases of Gorgond share the general chat channel. Getting this mount is half dedication and half luck.