Ob Nixilis of the Black Oath

+2: Each opponent loses 1 life. You gain life equal to the life lost this way.
−2: Create a 5/5 black Demon creature token with flying. You lose 2 life.
−8: You get an emblem with "{1}{B}, Sacrifice a creature: You gain X life and draw X cards, where X is the sacrificed creature's power."
Ob Nixilis of the Black Oath can be your commander.

Priest of the Blood Rite

When this creature enters, create a 5/5 black Demon creature token with flying.
At the beginning of your upkeep, you lose 2 life.

Phyrexian Denouncer

{T}, Sacrifice this creature: Target creature gets -1/-1 until end of turn.

Vindictive Lich

When this creature dies, choose one or more. Each mode must target a different player.
• Target opponent sacrifices a creature of their choice.
• Target opponent discards two cards.
• Target opponent loses 5 life.

Dying Wail

Enchant creature
When enchanted creature dies, target player discards two cards.

Sol Ring

Pillar Tombs of Aku

At the beginning of each player's upkeep, that player may sacrifice a creature of their choice. If that player doesn't, they lose 5 life and you sacrifice this enchantment.

Polluted Mire

This land enters tapped.
{T}: Add {B}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Death Watch

Enchant creature
When enchanted creature dies, its controller loses life equal to its power and you gain life equal to its toughness.

Necrotic Plague

Enchant creature
Enchanted creature has "At the beginning of your upkeep, sacrifice this creature."
When enchanted creature dies, its controller chooses target creature one of their opponents controls. Return this card from its owner's graveyard to the battlefield attached to that creature.

Shadows of the Past

Whenever a creature dies, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{4}{B}: Each opponent loses 2 life and you gain 2 life. Activate only if there are four or more creature cards in your graveyard.

Demonic Rising

At the beginning of your end step, if you control exactly one creature, create a 5/5 black Demon creature token with flying.

Phyrexian Defiler

{T}, Sacrifice this creature: Target creature gets -3/-3 until end of turn.

Barad-dûr

Barad-dûr enters tapped unless you control a legendary creature.
{T}: Add {B}.
{X}{X}{B}, {T}: Amass Orcs X. Activate only if a creature died this turn.

Ardyn, the Usurper

Demons you control have menace, lifelink, and haste.
Starscourge — At the beginning of combat on your turn, exile up to one target creature card from a graveyard. If you exiled a card this way, create a token that's a copy of that card, except it's a 5/5 black Demon.

Archfiend's Vessel

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
When this creature enters, if it entered from your graveyard or you cast it from your graveyard, exile it. If you do, create a 5/5 black Demon creature token with flying.

Bojuka Bog

This land enters tapped.
When this land enters, exile target player's graveyard.
{T}: Add {B}.

Mark of the Oni

Enchant creature
You control enchanted creature.
At the beginning of the end step, if you control no Demons, sacrifice this Aura.

Fume Spitter

Sacrifice this creature: Put a -1/-1 counter on target creature.

Lightless Evangel

Whenever you sacrifice another creature or artifact, put a +1/+1 counter on this creature.

Bonecaller Cleric

{3}{B}, Sacrifice this creature: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Demonic Covenant

Whenever one or more Demons you control attack a player, you draw a card and lose 1 life.
At the beginning of your end step, create a 5/5 black Demon creature token with flying, then mill two cards. If two cards that share all their card types were milled this way, sacrifice this enchantment.

Failed Conversion

Enchant creature
Enchanted creature gets -4/-4.
When enchanted creature dies, surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Plumb the Forbidden

As an additional cost to cast this spell, you may sacrifice one or more creatures. When you do, copy this spell for each creature sacrificed this way.
You draw a card and you lose 1 life.

Feral Ghoul

Menace
Whenever another creature you control dies, put a +1/+1 counter on this creature.
When this creature dies, each opponent gets a number of rad counters equal to its power.

Necrogen Communion

Enchant creature you control
Enchanted creature has toxic 2. (Players dealt combat damage by it also get two poison counters.)
When enchanted creature dies, return that card to the battlefield under your control.

Relic Vial

{2}, {T}, Sacrifice a creature: Draw a card.
As long as you control a Cleric, this artifact has "Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life."

Blood Pet

Corpse Hauler

{2}{B}, Sacrifice this creature: Return another target creature card from your graveyard to your hand.

Death Cultist

Sacrifice this creature: Target player loses 1 life and you gain 1 life.

Scavenger Drake

Flying
Whenever another creature dies, you may put a +1/+1 counter on this creature.

Bone Shards

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

Scavenger's Talent

(Gain the next level as a sorcery to add its ability.)
Whenever one or more creatures you control die, create a Food token. This ability triggers only once each turn.
{1}{B}: Level 2
Whenever you sacrifice a permanent, target player mills two cards.
{2}{B}: Level 3
At the beginning of your end step, you may sacrifice three other nonland permanents. If you do, return a creature card from your graveyard to the battlefield with a finality counter on it.

Overeager Apprentice

Discard a card, Sacrifice this creature: Add {B}{B}{B}.

Charcoal Diamond

This artifact enters tapped.
{T}: Add {B}.

Altar's Reap

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

Lurebound Scarecrow

As this creature enters, choose a color.
When you control no permanents of the chosen color, sacrifice this creature.

Withercrown

Enchant creature
Enchanted creature has base power 0 and has "At the beginning of your upkeep, you lose 1 life unless you sacrifice this creature."

Dreadhound

When this creature enters, mill three cards. (Put the top three cards of your library into your graveyard.)
Whenever a creature dies or a creature card is put into a graveyard from a library, each opponent loses 1 life.

Dread Return

Return target creature card from your graveyard to the battlefield.
Flashback—Sacrifice three creatures. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Demonic Vigor

Enchant creature
Enchanted creature gets +1/+1.
When enchanted creature dies, return that card to its owner's hand.

Phyrexian Plaguelord

{T}, Sacrifice this creature: Target creature gets -4/-4 until end of turn.
Sacrifice a creature: Target creature gets -1/-1 until end of turn.

Smothering Abomination

Devoid (This card has no color.)
Flying
At the beginning of your upkeep, sacrifice a creature.
Whenever you sacrifice a creature, draw a card.

Screams from Within

Enchant creature
Enchanted creature gets -1/-1.
When enchanted creature dies, return this card from your graveyard to the battlefield.

Bloodsoaked Altar

{T}, Pay 2 life, Discard a card, Sacrifice a creature: Create a 5/5 black Demon creature token with flying. Activate only as a sorcery.

Phyrexian Debaser

Flying
{T}, Sacrifice this creature: Target creature gets -2/-2 until end of turn.

Sadistic Glee

Enchant creature
Whenever a creature dies, put a +1/+1 counter on enchanted creature.

Eaten Alive

As an additional cost to cast this spell, sacrifice a creature or pay {3}{B}.
Exile target creature or planeswalker.

Nurgle's Rot

Enchant creature an opponent controls
When enchanted creature dies, return this card to its owner's hand and you create a 1/3 black Demon creature token named Plaguebearer of Nurgle.

Yoke of the Damned

Enchant creature
When a creature dies, destroy enchanted creature.

Unholy Indenture

Enchant creature
When enchanted creature dies, return that card to the battlefield under your control with a +1/+1 counter on it.

Rapacious Guest

Menace
Whenever one or more creatures you control deal combat damage to a player, create a Food token.
Whenever you sacrifice a Food, put a +1/+1 counter on this creature.
When this creature leaves the battlefield, target opponent loses life equal to its power.

Popular Egotist

{1}{B}, Sacrifice another creature or enchantment: This creature gains indestructible until end of turn. Tap it. (Damage and effects that say "destroy" don't destroy it.)
Whenever you sacrifice a permanent, target opponent loses 1 life and you gain 1 life.

Myriad Landscape

This land enters tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice this land: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.

Basal Thrull

{T}, Sacrifice this creature: Add {B}{B}.

Prowling Geistcatcher

Whenever you sacrifice another creature, exile it. If that creature was a token, put a +1/+1 counter on this creature.
When this creature leaves the battlefield, return each card exiled with it to the battlefield under your control.

Tragic Slip

Target creature gets -1/-1 until end of turn.
Morbid — That creature gets -13/-13 until end of turn instead if a creature died this turn.

Mortuary Mire

This land enters tapped.
When this land enters, you may put target creature card from your graveyard on top of your library.
{T}: Add {B}.

Swamp

Body Count

Spectacle {B} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
Draw a card for each creature that died under your control this turn.

Village Rites

Gixian Infiltrator

Whenever you sacrifice another permanent, put a +1/+1 counter on this creature.

Apprentice Necromancer

{B}, {T}, Sacrifice this creature: Return target creature card from your graveyard to the battlefield. That creature gains haste. At the beginning of the next end step, sacrifice it.

Arcane Signet

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

Unhallowed Pact

Enchant creature
When enchanted creature dies, return that card to the battlefield under your control.

Skirsdag High Priest

Morbid — {T}, Tap two untapped creatures you control: Create a 5/5 black Demon creature token with flying. Activate only if a creature died this turn.

Witch's Cottage

({T}: Add {B}.)
This land enters tapped unless you control three or more other Swamps.
When this land enters untapped, you may put target creature card from your graveyard on top of your library.

Necrosynthesis

Enchant creature
Enchanted creature has "Whenever another creature dies, put a +1/+1 counter on this creature."
When enchanted creature dies, look at the top X cards of your library, where X is its power. Put one of those cards into your hand and the rest on the bottom of your library in a random order.

Quest for the Gravelord

Whenever a creature dies, you may put a quest counter on this enchantment.
Remove three quest counters from this enchantment and sacrifice it: Create a 5/5 black Zombie Giant creature token.

Venomcrawler

Lifelink
Devourer of Souls — Whenever another creature dies, put a +1/+1 counter on this creature.

Minion's Return

Flash
Enchant creature
When enchanted creature dies, return that card to the battlefield under your control.