Trading Card Game item obtained from using the redemption code on a rare card from the expansion "War of the Ancients." The code on the card must first be redeemed here, then the follow-up code redeemed in-game by speaking with Landro Longshot in Booty Bay.
The card may be bought from several places, but take special care that the website is reputable. My preferred websites are WoWTCGLoot.com followed by WoWLootCards.com.
As for the item itself: The spell is considered a transformation, not a shapeshift, so your character will still be able to mount and behave as normal.