Viscera Seer: Early game sac outlet. We like our sac outlets to be free to activate, and Seer does that. He comes out early enough, and helps set up our draws by scrying away cards we don't want.
Dusk Legion Zealot/Phyrexian Rager: Early card draw on ETB creatures. We don't do much in the earlier turns, so these will help us to dig deeper into our deck for things to do later on.
Mesmeric Fiend: A new addition to the deck. I wanted to have a more proactive approach to removal, so what better way to do that than take it straight from the hand. Fiend also exiles the card, so it's permanent removal, for the most part, and hits any nonland card. Much like Faceless Butcher, its two effects are separate, so after it enters and triggers, you sacrifice it, its LTB effect will trigger, returning nothing, and then the ETB effect resolves and exiles the card indefinitely.
Soldevi Adnate: Sac outlet that generates an amount of equal to the CMC of the sacrificed creature. This will basically pay Gonti's printed cost, and all we need to pay for is the commander tax. Otherwise, we sac another creature to pay for other spells.
Crypt Ghast: Staple card in any mono black deck. Doubles the amount of mana your Swamps produce. Has the added effect of draining each opponent and you gaining that much life at the cost of each time you cast a spell. With Urborg, Tomb of Yawgmoth out, tapping your nonbasic lands for will net .
Dimir House Guard: Mainly used as a tutor. There are 14 cards with a CMC of 4, meaning there is no end to what this guy can grab such as removal, card draw, or utility. Can also use him as a body with a built-in sac outlet.
Entomber Exarch: Recursion and proactive removal on an ETB creature. Allows us to pull creatures from the graveyard to reuse, or it gets problematic noncreature spells from an opponent. The versatility on this creature is very nice.
Erebos, God of the Dead: A source of indestructible card draw. Prevents opponent’s from using any lifegain shenanigans. When we have enough devotion, we get ourselves a 5/7 indestructible beater.
Faceless Butcher/Ravenous Chupacabra: Removal on a stick for any creature an opponent controls. Another ETB effect to abuse with Panharmonicon/Conjurer's Closet. Butcher can also be used in conjunction with a sac outlet to permanently exile a creature due to the separated clause in its effect.
Solemn Simulacrum: Sad Robot! On ETB, he allows us to search up a land. On death, he lets us draw a card . Both effects we love in this deck.
Thought-Knot Seer: This card is in the same vein as Mesmeric Fiend. Used as proactive removal to get rid of threats straight from the hand. The downside is that it will give an opponent a free card draw when it leaves. It also has separate ETB/LTB triggers, so you can use a sac outlet to have the opponent draw a card first, and then exile any one of them, or use it politically and exile a card from one opponent, and give the card draw to another. It does require to cast, so be sure you have a nonblack producing land ready.
Gray Merchant of Asphodel: Big Daddy Gary! This guy gets to be bonkers if our devotion is high and we have Panharmonicon on the field. Even better when Conjurer's Closet is also out. Gains us life and drains our opponents. One of our win conditions in the deck.
Sidisi, Undead Vizier: Tutor on a stick. Doubles as a sac outlet for a creature so we can reanimate it to get more use out of an ETB effect. 4/6 with Deathtouch is nothing to scoff at either.
Duplicant: Colorless removal that exiles so it gets around indestructible creatures. Do note that he only copies P/T and Creature Type and not any abilities. If you go to exile a commander, and they choose to put it into the Command Zone instead, Duplicant will not copy the values as it is a replacement effect, so will enter as a 2/4 Shapeshifter. No worries though, as we can just sac him and reuse him later.
Grave Titan: 10 power across 3 three bodies for is pretty good, especially when one of those bodies is a 6/6 with deathtouch. Can be used to generate infinite zombies and mana, and is a part of a win condition for the deck.
Kokusho, the Evening Star: One of the Legendary Kamigawa dragons, and the best one if you ask me. Keep sacrificing him and bringing him back will eventually kill our opponents, so he is another win condition in the deck.
Noxious Gearhulk: Another piece of our removal package. Repeatable use as it is an ETB effect creature so it can be blinked or recurred. Can also hit our creatures if we want to bring them back from the graveyard.
Wurmcoil Engine: Wurmcoil helps alleviate the loss of life that mono black is known for. It is also part of an infinite mana engine that gets passed Torpor Orb-like effects, as it is a death trigger instead of an ETB trigger. Not only helps create infinite mana, but can also create infinite tokens as well.
Meteor Golem: Black has a hard time dealing with noncreatures. Oblivion Stone and Nevinyrral's Disk were used as ways of getting rid of these things. However, they hurt us as much as the opponent, if not more. Enter Meteor Golem. Our saving grace. He can destroy any nonland permanent. It's an ETB effect so it's abusable with Panharmonicon/Conjurer's Closet/Lifeline. He's a creature so he can be reanimated for multiple uses. By far the best card M19 has brought to this deck.
Rune-Scarred Demon: Another tutor on a stick. for a 6/6 flyer is still kinda hefty, but since it has an ETB effect of tutoring any card, he makes the cut in the deck as we can flicker with
Conjurer's Closet and bring him back from the graveyard.
Sepulchral Primordial: Recursion for opponents' creatures. Not the most powerful effects for cost, as some opponents may not even run creatures, but it can bring back up to three creatures (six if Panharmonicon is out).
Sheoldred, Whispering One: The big boss lady herself. Removal and recursion in one creature. She tends to paint a big target on her head, but if she sticks around, she can give you some pretty good value.