Based on the top 8 Pro Tour Theros deck of the same name
____Mainboard____
4x Desecration Demon: 2 devotion, creature control against aggro, serious threat against control.
2x Devour Flesh: get rid of a Blood Baron or keep yourself alive.
4x Doom Blade: probably the best creature removal in the set.
1x Erebos, God of the Dead: can become a 5/7 fairly easily, also slows Azorius control down quite a bit.
4x Gray Merchant of Asphodel: the only reason the deck is powerful, think corrupt, only less cost, and more damage.
4x Hero's Downfall: planeswalkers are extremely annoying, almost always saved for a planeswalker.
4x Lifebane Zombie: overall great creature, plus an extremely powerful ability, can easily get rid of the opponents biggest threat.
2x Mutavault: the original deck had 4, it is definitely the best utility land in the block, but I believe it hurts the deck's consistency.
1x Nykthos, Shrine to Nyx: the deck doesn't have anything to dump mana into, having one is sufficient.
2x Pack Rat: against any decks without a board wipe or immediate answers Pack Rat can get out of control, plus it grants an addition devotion per token.
4x Temple of Silence: solely for scrying, helps to prevent dead draws, until Black/Red scry lands come out it doesn't matter which combination of Black you use.
4x Thoughtseize: not like your opponent wanted to play magic anwyays. Can easily set your opponent back very far.
4x Underworld Connections: 2 devotion and draw power, although nowhere near as powerful as Necropotence, 1 life for 1 card is insane.
2x Whip of Erebos: you won't have many plays to make the first few turns besides Thoughtseize or Duress if you're lucky, the lifelink will help to keep you in the game. The unearth ability will allow you to bring back your creatures. Such as your merchant, dealing the same damage as if it were cast from your hand. Your zombie, still trashing their hand. Your rat, still with the ability to copy itself. Your demon, because Desecration Demon is evil.
___Sideboard___
1x Devour Flesh: extra creature control, side it in against Esper Control.
4x Duress: more hand hate, side it in against control in place of your Doom Blades.
1x Erebos, God of the Dead. side in against Azorius, Sphinx's Revelation is a very powerful card.
4x Mogis's Marauder: the original deck had 4x Xathrid Necromancer, although there were no other humans in the deck this was (probably) because it could block without losing much, getting a 2/2 back from losing a 2/2 as well as providing some kind of board wipe insurance. I put this in instead because I foresee blockers as being more of an issue, at least in the meta where I live, you may decide differently.
4x Pharika's Cure: very powerful against any type of aggro, a turn 2 solution to their early attacker is very helpful, since it will slow them through their loss of a creature and your gaining of 2 life.
1x Pithing Needle: turn 1 Pithing Needle name a key planeswalker you know to be in their deck now that you've played against them.
