Ironbound Wraithcharger

Its ethereal spirit is barely contained by its iron shell. The penultimate creation of Salanar the Horseman, these powerful steeds were once thought to have all been destroyed.

Riding Requirements:

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

Source:

Auzin in Dalaran (Northrend).
Cost: 5000
Only available during Timewalking

Notes:

This ghostly iron steed can be purchased from Auzin, a vendor by the fountain in Dalaran (Northrend), but only during Wrath of the Lich King Timewalking Events. Purchase requires Timewarped Badges, which are earned by running Timewalking Dungeons during the events, with a bonus 500 by handing in a quest item which drops at the end of your first dungeon for the event.

Introduced in:

Patch 6.2.2

Travel Mode:

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

Speed depends on your riding skill.

More info on Wowhead:

Ironbound Wraithcharger taught by Bridle of the Ironbound Wraithcharger