A death knight mounted on a Frost Wyrm. Not much to say about it. I recommend to use it as some type of advanced flying caster unit (no mesh changes to make it badass enough for a boss). Give credit and blah.
I'm making a more customized, detailed and badass version, but why not upload this as well.
UPDATE:
There it goes, guys. He's smaller, had feet and Attack Slam animation.
Keywords:
wotlk, death, knight, death knight, runeblade, frost, wyrm, frost wyrm, lich king, unholy, rider, mounted, flying, undead