Well, I built this dark deck, mostly based off something I used long ago, probably not very original:
8x Obsidian Pillar
5x Black Dragon
6x Devourer
3x Dusk Mantle
3x Steal
2x Nightfall
3x Drain Life
Mark of Darkness.
(Obviously, everything is unupped).
It just got me a rare spin (and a pharaoh) in silver - I'll start keeping stats now.
EDIT: This got slammed pretty hard - over 32 games, 13 wins, 19 losses, 3 EMs. Weaknesses were early Oty, early CC on the devourers, and obviously Sanctuary if you can't get early Steals.
Against mostly unupped decks it did very well (it was highly satisfying to completely shut down a fire deck from the beginning with quanta denial), but there were a surprising amount of close to fully upped decks. There were 2-3 mirror matches (I lost them all - the Arena bonuses make any mirror match an almost guaranteed loss), which also surprised me. The deck also takes a while to get going, so a rush with decent draws can win before you can get anything out.
Back to the drawing board.