1) Why does Michael call him "Blood of the Dragon, that old Serpent"
I believe Michael calls Marva "Blood of the Dragon" - leading to our speculation that since Dracula son of Drakul "started the Black Court as teenage rebellion", that Drakul is a half-dragon scion.
Yeah, it was Mavra, my bad. I think the actual quote you're referencing though is that Dracula "went to" the Black Court as a kind of teenage rebellion, though, he didn't "start" it -- the black court predates Dracula by a long while.
I'm pretty sure "Blood of the Dragon, that Old serpent," is a reference to Revelation 20:2 (KJV).
"And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,"I can see a few possibilities here. There's also a large possibility of forshadowing on Jim Butcher's part.
1) Michael was speaking metaphoricaly and just calling Marva evil in a really cool way.
2) Michael is implying that Drakul is either a dragon or spawn of a dragon
3) Michael is implying that Drakul is either the Devil or spawn of the Devil
4) Michael is implying that Drakul is the spawn of the Devil and a dragon. (Run fast, run far, don't look back, and hope you're wearing dark brown pants.
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