I don't know how, but I'm at an 81% winrate between ranks 15 and 10:

16 games and 13 victories.

Too bad I don't have time to test it more. In case anyone feels like trying to improve it, give it a go.

For the mulligan I try to keep a 1 drop and find EVIL Genius for the early board control + lackeys/additional resources generation.

Otherwise, make big boards with the Diseased Vulture and go "tall" with the Nethersoul Buster.

Enjoy!