Boldly, You Sought the Power of Ragnaros

Boldly, You Sought the Power of Ragnaros is a Feats of Strength achievement earned from defeating the updated 40-man version of Ragnaros in Molten Core during World of Warcraft's 10th anniversary.

The mount is mailed to you.

Though the mount was later added to the Black Market Auction House, the winning bidder will not get the achievement.