U/B mill with Phenax, God of Deception and big walls like Wall of Frost.
Doorkeeper can start the milling if I don't have a Phenax. Big walls like Wall of Frost, Hover Barrier and Murmuring Phantasm make great blockers and are even better for milling, particularly with Triton Tactics to make them even tankier, apply frost breath, and mill for more (untapping being highly relevant with Phenax).
After some deliberation, I decided on Swan Song as my protection spell for the combo, as I don't think creatures should really be much of a problem for this deck, and I hope most planeswalkers will be a bit too slow to stop me. The fact that only one blue needs to be kept open was also a big factor in this decision (and it should be a great card in a mirror... if that ever happens). Grisly Spectacle is purely for those rare scenarios where a creature can rapidly become too large for my walls. In those cases, the bonus mill should be quite relevant. I shouldn't be playing it too early, so I'm not too worried about the high CMC.
I've found Ashiok, Nightmare Weaver to be highly effective against both aggro and control decks. As my primary alternative win-con, I've decided to risk playing 4 in the hopes that my opponents will use everything to try and kill them, while the walls hold a solid defense (and I hopefully draw a Phenax). Similar reasoning for Jace, Memory Adept, although I couldn't rationalize playing four of such a high CMC.
I'm experimenting with Read the Bones as my draw card in place of Pilfered Plans as I hope to not be taking very much damage from creatures (so I should be able to afford the 2 pain), and Read the Bones is better for searching for Phenax than Divination or Pilfered Plans.
Some other options I am seriously considering are Crypt Incursion for stealing a lot of life, which might be highly relevant against decks like mono-B.Lazav, Dimir Mastermind has hexproof (yay) and counts as 4 devotion for Phenax. He can also morph into a creature with a lot more toughness as the milling begins, and could even constitute a win-con if he copies a good enough creature in my opponent's deck.Wight of Precinct Six could be a nice aggro card which gets bigger as the milling progresses, although it doesn't react well with Ashiok, Nightmare Weaver and to be good requires one to already be milling.Devour Flesh is a nice removal spell which can be cast on myself to sacrifice a wall and gain a lot of life, but I worry that it won't be good enough as spot removal because the opponent should have a lot of creatures to choose to sacrifice from.Omenspeaker might be nicer as an option to search for Phenax than Read the Bones as it has a body to mill with too.Elixir of Immortality and Psychic Spiral are good against the mirror (if that exists).
