Felsteel Annihilator

Forged deep within Hellfire Citadel by a mad blacksmith, the Felsteel Annihilator combines the metalworking knowledge of the Iron Horde with the chaotic fel energies of the Burning Legion into an unholy union of steel and flame.

Riding Requirements:

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

Source:

Archimonde in Hellfire Citadel (Draenor, Mythic).
The Black Market Auction House (rarely)

Introduced in:

Patch 6.2

Travel Mode:

Ground (+60% or +100% speed)
Flying (+150%, +280% or +310% speed)

Speed depends on your riding skill.

More info on Wowhead:

Felsteel Annihilator taught by Felsteel Annihilator