Reins of the Ashen Pandaren Phoenix

The Reins of the Ashen Pandaren Phoenix is a Pandaren Phoenix mount achievement reward.

Source
When you complete the achievement Challenge Conqueror: Silver, you will receive one Ancestral Phoenix Egg in the mail. This can be redeemed for a Ashen Pandaren Phoenix mount. To redeem, visit located in the Vale of Eternal Blossoms, outside the Seat of Knowledge.

Description
Both the name and color of this majestic phoenix are believed to symbolize rebirth.