Showcase your talents and find collaborators!
There are many recolours of WOW Classic TBC Gold these available via different methods. Then there are all the drake mounts from WotLK and Cata which are just recolours of rare spawn drops/reputation/achievement rewards.
There are other mounts of raid which I didn't list, like Glacial Tidestorm from mythic Jaina that is a reskin of the shaman class mount or Ny'alotha Allseer from mythical N'Zoth that is an reskin of a jellyfish mount.
It's a matter of what you mean when you say "reskin". The mythic mount of N'Zoth is just the jellyfish mount, Jaina mythic is only the mount of the shaman class, Gul'dan's mythic is the grumpus mount (I think at least) Shackled Ur'zul in mythical Argus is (I believe) the gryphon's skeletal mount that DKs receive.
The only "original at the time" mythical mount that I can think of is Archimonde's Felsteel Annihilator. The Sylvanas mythic mount is also a completely new kind of buy WOW TBC Classic Gold mount.