I know that zombie hype has largely died down but this is the deck I've been playing since Amonkhet was released and it is the most fun I've had with any deck in standard (and I've been playing since the 90's). This deck will truly make you feel like a necromancer!
So, first, to the most obvious question, why blue/black instead of mono-black or white/black?
The answer is a better board state. With the inclusion of Prized Amalgams and Gisa and Geralf, you will often have a better board state than either mono-b or w/b can muster. Most significantly, however, you fear no board-wipes. I was once fumigated 4(!) times in a single game and still won. Once you have Prized Amalgams and Dread Wanderers in your graveyard you couldn't care less about fumigate. I have found that the inclusion of Amalgams and G+G is stronger than the consistency of mono-b variants and stronger than the inclusion of Wayward Servant that white/black variants get.
This deck grinds for value like no other deck in standard. I have won a game at a Saturday Showdown with 1 Cryptbreaker, and just 2 basic land. The amount of favorable interactions is almost overwhelming.
If you are excited to play this deck but don't have the $$$ for 2 Liliana, the Last Hope, feel free to cut her from the list. Out of all the cards in the list she has felt the least necessary. PWs are always strong, but there are plenty of other solid cards to include. If I were to cut them from my list, I might replace them with Fatal Pushes or a Plague Belcher and another Miasmic Mummy.
Sideboard Choices:
The Liliana's Masteries are good and were mainboarded for a long while. The issue with them is that I'd end up pitching it to Cryptbreaker early or win before hitting 5 mana. They're better in certain matchups, and I generally board them in against control and other tribal decks (especially mirror).
Kalitas is for the mirror and any other deck that likes to play from the graveyard. It's also devastating against an aggro deck that wants to punish you with Scrapheap.
Dispossess is obviously for Aetherworks Marvel. If you manage to resolve it before they get their Marvel down, they are probably going to scoop.
Never//Return is wonderful in the mirror also, but primarily is in the sideboard because of superfriends decks.
Grasp is there for the Heart of Kiran/Gideon of the Trials/Avacyns that you might encounter, and you really need some instant speed removal in your sideboard. You could easily swap it out for Fatal Push, but I find that most things Fatal Push kills my zombies don't have trouble with or I'd rather be casting Dark Salvation.
