Awakened Mindborer

It may look menacing right now, but it's actually kind of cute when it's asleep.

Riding Requirements:

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

Source:

Sold by Lindormi <Mythic Keystones>
Cost: 1

Notes:

The Timelost Saddle required to purchase this mount is awarded to players after earning the current season's 'Keystone Myth' achievement, from obtaining a Mythic+ rating of 3400. It can be used to buy an achievement mount from any of the previous Mythic+ seasons, plus several previously-unused colour variants of these mounts. These are sold by Lindormi in the current expansion hub / capital. Currently, just one Saddle can be earned per season.

This mount was originally a Keystone Master achievement reward for Battle for Azeroth Season Four.