Astral Emperor's Serpent

After the unburdened Emperor Shaohao gave his final breath to protect his people, a golden serpent descended from the heavens to alight the emperor's spirit to the peaks of Kun-Lai Summit.

Riding Requirements:

This mount is available to all eligible characters on your account.
Level 10
Apprentice Riding (ground)
Expert Riding (flying)

Source:

Achievement: Vale of Eternal Blossoms

Notes:

This celestial serpent is awarded by a meta-achievement for completing two of four specific achievements during the Pandaria: Remix Timerunning event. The achievements relate to: completing Looking for Group Dungeons, defeating rare foes in the Vale of Eternal Blossoms, and reaching Exalted status with August Celestials or Golden Lotus.