In an interview with Icy Veins, Blizzard has revealed that Fyrakk will drop three different cosmetics, one mount, and two different manuscripts.
Mythic Fyrakk
On Mythic, Fyrakk will drop a mount! A Fire Owl mount, which will be the first non-dragon Dragonriding capable mount. While there isn’t an official preview, we have the following Fire Owl mount showing in the patch trailer, so that’s likely the appearance.