The Rubyshell Krolusk mount is a Horde-only mount tied to Warfront in World of Warcraft. It was added in the 8.1 patch as part of the Warfront rewards. It is not directly obtained by participating in Warfronts, but you can instead buy it for 200x Honorbound Service Medals.
The Honorbound Service Medals are rewarded when you do activities that are tied to either Honorbound as a faction, or Warfronts. You get them from the Honorbound Paragon Cache (by getting 10k extra rep after hitting Exalted), by doing World Quests when the Horde controls a Warfront zone, by winning the first Warfront per cycle, and by winning Faction Assaults.
Grinding the Honorbound Servide Medals takes a long time, since there is a cap on how many you can get daily. You will typically get 5-12 Honorbound Servide Medals daily, with less when you don't control any Warfront zones. So getting the 200 Honorbound Servide Medals required can take a while, but you should be able to do it within a few weeks.
Once you have enough Honorbound Servide Medals, buy the mount from Provisioner Mukra in Dazar'alor. All the Service Medals must be gotten by a single character for you to buy it, but you can use the mount on any character after you have learned it.