The Hippogryph Hatchling item summons and dismisses a Hippogryph Hatchling, a baby hippogryph Companion that follows you around, meaning it is a non-combat pet and will not aid you in battle.
The Hippogryph Hatchling is available to those who receive the Thunderhead Hippogryph
card in the World of Warcraft Trading Card Game
that has the "scratch off gently" strip. Once you scratch and reveal the code, you can turn it in to Landro Longshot
in Booty Bay [28, 75]
who will give you your Hippogryph Hatchling. It is also available via the Black Market Auction House
A sample Hippogryph Hatchling exists as a neutral level 1 beast near Landro Longshot.