I Was Promised a Pony

The I Was Promised a Pony achievement is available during the Darkmoon Faire on Darkmoon Island.

Details
One of the areas in the Darkmoon Faire is a petting zoo not far from the boardwalk. In the petting zoo are some animals, and one is the Darkmoon Pony. The mouse cursor converts to a green vehicle entry arrow when you mouse over the pony. Click to ride the pony and achieve.