Wretched Fel Bat

Its bracers seem to be a bit snug.

Riding Requirements:

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

Source:

Sold by Hemet Nesingwary XVII in Infinite Bazaar, Dalaran (Legion Remix).
Cost: 10 000

Notes:

This mount can only be purchased during Legion Remix - a time-limited event held on specially-dedicated servers, using accelerated levelling and some changes to features. The 'Bronze' currency required for this mount can be earned in large amounts from various Remix activities.