Font of Agonies

Whenever you pay life, put that many blood counters on Font of Agonies.
{1}{B}, Remove four blood counters from Font of Agonies: Destroy target creature.

Harvester of Souls

Deathtouch
Whenever another nontoken creature dies, you may draw a card.

Meteor Golem

When Meteor Golem enters the battlefield, destroy target nonland permanent an opponent controls.

Sepulchral Primordial

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
When Sepulchral Primordial enters the battlefield, for each opponent, you may put up to one target creature card from that player's graveyard onto the battlefield under your control.

Syr Konrad, the Grim

Whenever another creature dies, or a creature card is put into a graveyard from anywhere other than the battlefield, or a creature card leaves your graveyard, Syr Konrad, the Grim deals 1 damage to each opponent.
{1}{B}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Disciple of Bolas

When Disciple of Bolas enters the battlefield, sacrifice another creature. You gain X life and draw X cards, where X is that creature's power.

Demon's Disciple

When Demon's Disciple enters the battlefield, each player sacrifices a creature or planeswalker.

Unmarked Grave

Search your library for a nonlegendary card, put that card into your graveyard, then shuffle.

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Ashnod's Altar

Living Death

Each player exiles all creature cards from their graveyard, then sacrifices all creatures they control, then puts all cards they exiled this way onto the battlefield.

Noxious Gearhulk

Menace
When Noxious Gearhulk enters the battlefield, you may destroy another target creature. If a creature is destroyed this way, you gain life equal to its toughness.

Swamp

Sivriss, Nightmare Speaker

{T}, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.)
Choose a Background (You can have a Background as a second commander.)

Sewer Nemesis

As Sewer Nemesis enters the battlefield, choose a player.
Sewer Nemesis's power and toughness are each equal to the number of cards in the chosen player's graveyard.
Whenever the chosen player casts a spell, that player mills a card.

Ravenous Chupacabra

When Ravenous Chupacabra enters the battlefield, destroy target creature an opponent controls.

Butcher of Malakir

Flying
Whenever Butcher of Malakir or another creature you control dies, each opponent sacrifices a creature.

Grim Haruspex

Morph {B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
Whenever another nontoken creature you control dies, draw a card.

Fleshbag Marauder

When Fleshbag Marauder enters the battlefield, each player sacrifices a creature.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Stitch Together

Return target creature card from your graveyard to your hand.
Threshold — Return that card from your graveyard to the battlefield instead if seven or more cards are in your graveyard.

Cabal Stronghold

{T}: Add {C}.
{3}, {T}: Add {B} for each basic Swamp you control.

Ayara, First of Locthwain

Whenever Ayara, First of Locthwain or another black creature enters the battlefield under your control, each opponent loses 1 life and you gain 1 life.
{T}, Sacrifice another black creature: Draw a card.

Sign in Blood

Target player draws two cards and loses 2 life.

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Geth, Lord of the Vault

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
{X}{B}: Put target artifact or creature card with mana value X from an opponent's graveyard onto the battlefield under your control tapped. Then that player mills X cards.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Solemn Simulacrum

When Solemn Simulacrum enters the battlefield, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.
When Solemn Simulacrum dies, you may draw a card.

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters the battlefield, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Sol Ring

Hostile Negotiations

Exile the top three cards of your library in a face-down pile, then exile the top three cards of your library in another face-down pile. Look at the cards in each pile, then turn a pile of your choice face up. An opponent chooses one of those piles. Put all cards in the chosen pile into your hand and the rest into your graveyard. You lose 3 life.

Corpse Connoisseur

When Corpse Connoisseur enters the battlefield, you may search your library for a creature card, put that card into your graveyard, then shuffle.
Unearth {3}{B} ({3}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Viscera Seer

Sacrifice a creature: Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Stitcher's Supplier

When Stitcher's Supplier enters the battlefield or dies, mill three cards.

Perpetual Timepiece

{T}: Mill two cards.
{2}, Exile Perpetual Timepiece: Shuffle any number of target cards from your graveyard into your library.

Phyrexian Arena

At the beginning of your upkeep, you draw a card and you lose 1 life.

Thrilling Encore

Put onto the battlefield under your control all creature cards in all graveyards that were put there from the battlefield this turn.

Charcoal Diamond

Charcoal Diamond enters the battlefield tapped.
{T}: Add {B}.

Cemetery Tampering

Hideaway 5 (When this enchantment enters the battlefield, look at the top five cards of your library, exile one face down, then put the rest on the bottom in a random order.)
At the beginning of your upkeep, you may mill three cards. Then if there are twenty or more cards in your graveyard, you may play the exiled card without paying its mana cost.

Dictate of Erebos

Flash
Whenever a creature you control dies, each opponent sacrifices a creature.

Diabolic Intent

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a card, put that card into your hand, then shuffle.

Vile Entomber

Deathtouch
When Vile Entomber enters the battlefield, search your library for a card, put that card into your graveyard, then shuffle.

Cabal Therapy

Choose a nonland card name. Target player reveals their hand and discards all cards with that name.
Flashback—Sacrifice a creature. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Chain of Smog

Target player discards two cards. That player may copy this spell and may choose a new target for that copy.

Village Rites

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Extractor Demon

Flying
Whenever another creature leaves the battlefield, you may have target player mill two cards.
Unearth {2}{B} ({2}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Necron Deathmark

Flash
Synaptic Disintegrator — When Necron Deathmark enters the battlefield, destroy up to one target creature and target player mills three cards.

Chainer, Dementia Master

All Nightmares get +1/+1.
{B}{B}{B}, Pay 3 life: Put target creature card from a graveyard onto the battlefield under your control. That creature is black and is a Nightmare in addition to its other creature types.
When Chainer, Dementia Master leaves the battlefield, exile all Nightmares.

Out of the Tombs

At the beginning of your upkeep, put two eon counters on Out of the Tombs, then mill cards equal to the number of eon counters on it.
If you would draw a card while your library has no cards in it, instead return a creature card from your graveyard to the battlefield. If you can't, you lose the game.

Awaken the Erstwhile

Each player discards all the cards in their hand, then creates that many 2/2 black Zombie creature tokens.

Abhorrent Overlord

Flying
When Abhorrent Overlord enters the battlefield, create a number of 1/1 black Harpy creature tokens with flying equal to your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
At the beginning of your upkeep, sacrifice a creature.

Wayfarer's Bauble

{2}, {T}, Sacrifice Wayfarer's Bauble: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Yahenni, Undying Partisan

Haste
Whenever a creature an opponent controls dies, put a +1/+1 counter on Yahenni, Undying Partisan.
Sacrifice another creature: Yahenni gains indestructible until end of turn.

Bog Witch

Altar of Dementia

Sacrifice a creature: Target player mills cards equal to the sacrificed creature's power.

Crypt Ghast

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional {B}.

Gonti, Lord of Luxury

Deathtouch
When Gonti, Lord of Luxury enters the battlefield, look at the top four cards of target opponent's library, exile one of them face down, then put the rest on the bottom of that library in a random order. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.

Animate Dead

Enchant creature card in a graveyard
When Animate Dead enters the battlefield, if it's on the battlefield, it loses "enchant creature card in a graveyard" and gains "enchant creature put onto the battlefield with Animate Dead." Return enchanted creature card to the battlefield under your control and attach Animate Dead to it. When Animate Dead leaves the battlefield, that creature's controller sacrifices it.
Enchanted creature gets -1/-0.

Angel of Suffering

Flying
If damage would be dealt to you, prevent that damage and mill twice that many cards.

Dark Deal

Each player discards all the cards in their hand, then draws that many cards minus one.

Overwhelming Remorse

This spell costs {1} less to cast for each creature card in your graveyard.
Exile target creature or planeswalker.

Night's Whisper

Bone Shards

As an additional cost to cast this spell, sacrifice a creature or discard a card.
Destroy target creature or planeswalker.

Reckoner's Bargain

As an additional cost to cast this spell, sacrifice an artifact or creature.
You gain life equal to the sacrificed permanent's mana value. Draw two cards.