I DID IT!!! MOTHERFUCKING ANGELIT GET!!
Took me like 7 stones altogether, but I fucking did it.
I ran Dark Meta, Byakko, Hanzo, Lilith, Echidna with a Dark Meta sub. I got a rank up stam refresh at 3am and ran it 3 times until I finally got a favorable first turn on the 4th attempt. This team requires at least 5 dark orbs on the board, preferably 8 to survive wave 1, which is why max skilled Hanzo is so important) It went very smoothly, popped a stone on the preemptive and stalled on the Tamadra, and then wave 4 hit. Popped Byakko and Hanzo, and blasted the board, then popped Echidna. This was the result.
4 turns might be enough to whittle down that much HP as long as I don't heal up by accident, right? WRONG.
Close enough. I Lilith poisoned, spent two stones, and 1xed him into the ground. Done with this godforsaken dungeon, at least for now.