Actually, we do know a bit about the dragon at the party. His name was Ferrovax, he was dressed as a Roman centurion (not an outfit-- genuine armor from Roman times) and was pretending to smoke a cigarette to cover the fact he kept blowing out smoke from his mouth.

Also, Word of Jim is that dragons in the Dresdenverse are enormously powerful. Jimmy B said Ferrovax could take on Mab and win. They are forces of the universe, apparently.

And Michael killed one. Michael is awesome.