Smoldering Ember Wyrm

Arcanagos sought to turn Medivh away from experiments into the arcane, but the influence of Sargeras had corrupted the wizard too deeply, and the great dragon paid for the transgression with eternal, burning agony.

Riding Requirements:

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

Source:

Nightbane in Return to Karazhan.

Notes:

This mount drops from Nightbane in the Return to Karazhan dungeon.

Drop chance: Blizzard confirmed that the chance of this mount appearing is 20% multiplied by the number of players in your group that are eligible for loot (i.e. not loot-locked for that week). Party members who already have the mount still add to the drop chance, though they cannot receive it again. So, if you have 5 members in your party who are eligible for loot there's a 100% chance that the mount will drop for someone who doesn't already have it, and if only one member of a party of 5 doesn't have this mount then they're guaranteed it. But if you only have three players in your group and one is loot-locked, the chance drops to (3-1) x 20 = 40% that one eligible player will receive it. This loot rule hasn't changed in Battle for Azeroth.

Introduced in:

Patch 7.1

Travel Mode:

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

Speed depends on your riding skill.

More info on Wowhead:

Smoldering Ember Wyrm taught by Smoldering Ember Wyrm