This deck relies on a four card combo: Ayara, First of Locthwain Paradox Engine Relentless Dead Nyx Lotus
Get all four in play. Tap Nyx Lotus for 5+ black mana. Tap Ayara for her ability, sacrificing Relentless Dead and drawing a card. Using the 5+ black mana from Nyx Lotus, pay B to return Relentless Dead to hand. Recast Relentless Dead using BB still remaining from the Lotus, netting at least two black mana. Ayara's ability will trigger when Relentless Dead ETBs, draining 1 from the opponent. Paradox Engine triggers when you cast the Dead, untapping Ayara and Nyx Lotus. This combo can be repeated as long as you have cards in your library, so you can kill your opponent with Ayara damage before you run out of cards in your library.
In the event you can't combo off enough because your opponent has more life than you have cards in library? Twilight Prophet and Liliana Vess can provide a win anyway, along with whatever incidental damage you were able to inflict (or that your opponent inflicted on themself). This deck runs Inverter of Truth in the sideboard as well -- in case the "shuffle your graveyard into your library" effect is relevant to allow you to combo off. You will need to do this while Relentless Dead is in play to avoid shuffling it away.
Much of the deck is dedicated to helping you find the combo or stay alive long enough to use it. A suite of removal and board wipes can destroy enemy creatures trying to kill you. Thaumatic Compass can sort lands out of your deck, and once it flips it can invalidate an enemy creature every turn. Liliana Vess can tutor up a combo piece and attack your opponent's hand, while Dark Realms can sort all the lands out of your deck with ease as well as function as removal, or even score you a win out of nowhere with a Twilight Prophet on board.
The sideboard switches out some removal pieces with the catch-all Murder and the legendary-focused Price of Fame. Doom Blade can only hit nonblack creatures, Ultimate Price can only hit monocolored, and Cast Down can only hit nonlegendary. An opponent who runs black creatures, multicolored creatures, or legendary creatures can trouble your removal suite otherwise. Meteor Golem is the only access nonblack has to artifact or enchantment hate, and Thoughtseize can hit problematic cards in hand. Inverter comes in against decks that gain life, to avoid the possibility of your combo not being enough to kill them.
