Blackrock Warsaber

Riding Requirements:

This mount is available to all eligible characters on your account.
Level 10
Apprentice Riding

Notes:

This mount is a reward from the Warcraft 30th Anniversary Direct event, from 13 November, 10:00 am PST, until 11 December, 10:00 am PST. You can earn it by watching Warcraft 30th Anniversary Direct content on participating Twitch or TikTok channels (note: apparently not YouTube, although it was originally advertised).

The requirements for receiving the rewards vary between media:

For Twitch you must link your social media account to your Battle.net account and then watch at least 20 minutes of participating content.
For TikTok you must watch at least 3 minutes of participating content and receive a code that you can redeem in your Battle.net account page.
For full details of what's required, see Warcraft 30th Anniversary Direct page.