Were you looking for the  Vengeful Nether Drake Feats of Strength achievement?

• Vengeful Nether Drake
• Item Level 70Disenchants into:
  Not disenchantable
• Binds when picked up
• Unique


• Mount
• Requires Level 70
• Requires Riding (300)
• Use:Teaches you how to summon this mount. This is a flying mount.

Qualifiers for this mount should also get the  Vengeful Nether Drake Feats of Strength achievement.

Source

The Vengeful Nether Drake is the reward for players in the top 0.5% of arena teams per battlegroup at the end of Season 3.

External links

• Battle.net (EU)
• Wowhead
• Thottbot
• WoWDB