This deck is all about punishing our opponents for having a hand by either making them get rid of it or taking damage through draws. Key to this deck is the underrated and neglected Waste Not.
This enchantment is a powerhouse with any discard engine backing it. Opponent discards a creature and I get a free Zombie? Done. Lose a land and I get free mana? Sure. Dump anything else and I get to draw a card? Hell. To. The. Yes. To get all these goodies we're relying on four sources of discard: Thoughtseize, Mind Rot, Black Cat and Liliana Vess.
Now, we can't simply rely on discards to win us the game (no The Rack or Shrieking Affliction in this format). So while we're picking apart our opponents hand we must punish them for trying to refill it. Enter Fate Unraveler. Guaranteed 1 point of damage per turn, this old hag can really do damage against any draw spells our opponent uses to refill their hand after they've lost it to play or discard spells. For big damage, Master of the Feast is our "late game" bomb ( for a 5/5 flyer!?), whose supposed disadvantage of drawing our opponents cards complements nicely with Unraveler to get in that extra bit of damage. Finally, Typhoid Rats and Pharika's Chosen buy us the time we need to build up our engine.
~ Remaining Spell-base ~
Sign in Blood: Supplements the need to refill an opponents hand (or ours!) with the added benefit of dinging them for at least 2 life, 4 if we have an Unraveler out.
Whip of Erebos: Being a Black Mage hurts. A lot. Between sign in blood, thoughtseize, Polluted Delta, and our opponents we're taking a lot of damage in the early game. By whipping it good we can recoup a lot of that life and even make use of our creatures who departed us before their time.
Hero's Downfall: It's downfall, you know why it's here.
~ Sideboard ~
Here's the TL;DR version
Perilous Vault: For decks that deal in lots of noncreature permanents.
Cruel Feeding: Specifically for burn decks, though could be useful against aggro too. For when we need to gain life FAST.
Bile Blight
+
Drown in Sorrow
: Definitely for aggro/tokens, 'nuff said.
Erebos, God of the Dead: For any pesky lifegain shenanigans. Drawing more cards is always nice too.
Stain the Mind: Really for Jeskai ascendancy but also useful against control decks with only one or two win conditions.
Phyrexian Revoker: Superfriends beware.
Tormod's Crypt: Lots of delve in the meta right now, Most people don't see this one coming.
Thanks for the read, comments, suggestions, and +1s. I'm always looking to improve decks and never consider mine "finished," so all feedback is most welcome. If you enjoyed this ride on the Hate Train and want me to take a look at your deck I'd be more than happy too, just let me know!
Cheers.