During the Dragonflight Beta, a fifth Dragonriding mount was datamined, but it never made it live previously – All we knew about it besides datamining was the name, Winding Slitherdrake. The Winding Slitherdrake is finally making its debut in Patch 10.1, Embers of Neltharion!
You can check all known customizations from the Dragonflight Beta on our Dressing Room!