This mount is from a TCG loot card from the "Throne of the Tides" expansion.
The name of the loot card is Wasteland Tallstrider. To redeem the code on the loot card: you'll need to visit WoW's Promotion page, redeem the 25-digit code, copy or write down the second code given to you, log into the game and visit Landro Longshot.
The game item may be traded to another player.
As always, be very wary of deals that sound too good to be true - because they always are. If you want to purchase the WoW TCG loot card, make certain to buy from a reputable website.