The Balrog, Flame of Udûn

Trample
When a legendary creature an opponent controls dies, put The Balrog on the bottom of its owner's library.

Rakdos, the Showstopper

Flying, trample
When Rakdos enters, flip a coin for each creature that isn't a Demon, Devil, or Imp. Destroy each creature whose coin comes up tails.

Ob Nixilis, Unshackled

Flying, trample
Whenever an opponent searches their library, that player sacrifices a creature of their choice and loses 10 life.
Whenever another creature dies, put a +1/+1 counter on Ob Nixilis.

Defiler of Souls

Flying
At the beginning of each player's upkeep, that player sacrifices a monocolored creature of their choice.

Shadowgrange Archfiend

When this creature enters, each opponent sacrifices a creature with the greatest power among creatures they control. You gain life equal to the greatest power among creatures sacrificed this way.
Madness—{2}{B}, Pay 8 life. (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Bloodletter of Aclazotz

Flying
If an opponent would lose life during your turn, they lose twice that much life instead. (Damage causes loss of life.)

Valgavoth, Harrower of Souls

Flying
Ward—Pay 2 life.
Whenever an opponent loses life for the first time during each of their turns, put a +1/+1 counter on Valgavoth and draw a card.

Havoc Demon

Flying
When this creature dies, all creatures get -5/-5 until end of turn.

Demon of Loathing

Flying, trample
Whenever this creature deals combat damage to a player, that player sacrifices a creature of their choice.

Spiteful Prankster

During your turn, this creature has first strike.
Whenever another creature dies, this creature deals 1 damage to target player or planeswalker.

Mayhem Devil

Whenever a player sacrifices a permanent, this creature deals 1 damage to any target.

Perforating Artist

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Raid — At the beginning of your end step, if you attacked this turn, each opponent loses 3 life unless that player sacrifices a nonland permanent of their choice or discards a card.

Raphael, Fiendish Savior

Flying
Other Demons, Devils, Imps, and Tieflings you control get +1/+1 and have lifelink.
At the beginning of each end step, if a creature card was put into your graveyard from anywhere this turn, create a 1/1 red Devil creature token with "When this token dies, it deals 1 damage to any target."

Venomcrawler

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

Chaos Imps

Flying
Unleash (You may have this creature enter with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)
This creature has trample as long as it has a +1/+1 counter on it.

Archfiend of Sorrows

Flying
When this creature enters, creatures your opponents control get -2/-2 until end of turn.
Unearth {3}{B}{B} ({3}{B}{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.)

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.

Ravenous Skirge

Flying
Whenever this creature attacks, it gets +2/+0 until end of turn.

Chain Devil

Animate Chains — When this creature enters, each player sacrifices a nontoken creature of their choice.

The Balrog, Durin's Bane

This spell costs {1} less to cast for each permanent sacrificed this turn.
Haste
The Balrog can't be blocked except by legendary creatures.
When The Balrog dies, destroy target artifact or creature an opponent controls.

Spirit of the Night

Flying, trample, haste, protection from black
Spirit of the Night has first strike as long as it's attacking.

Vault Skirge

({B/P} can be paid with either {B} or 2 life.)
Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Herald of Anguish

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Flying
At the beginning of your end step, each opponent discards a card.
{1}{B}, Sacrifice an artifact: Target creature gets -2/-2 until end of turn.

Vexing Devil

When this creature enters, any opponent may have it deal 4 damage to them. If a player does, sacrifice this creature.

Flayer of the Hatebound

Undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.)
Whenever this creature or another creature enters from your graveyard, that creature deals damage equal to its power to any target.

Soulcage Fiend

When this creature dies, each player loses 3 life.

Dance with Devils

Create two 1/1 red Devil creature tokens. They have "When this token dies, it deals 1 damage to any target."

Devils' Playground

Create four 1/1 red Devil creature tokens. They have "When this token dies, it deals 1 damage to any target."

Bloodcrusher of Khorne

Trample
Devastating Charge — Other creatures you control have trample.

Dread Cacodemon

When this creature enters, if you cast it from your hand, destroy all creatures your opponents control, then tap all other creatures you control.

Taborax, Hope's Demise

Flying
Taborax has lifelink as long as it has five or more +1/+1 counters on it.
Whenever another nontoken creature you control dies, put a +1/+1 counter on Taborax. If that creature was a Cleric, you may draw a card. If you do, you lose 1 life.

Reiver Demon

Flying
When this creature enters, if you cast it from your hand, destroy all nonartifact, nonblack creatures. They can't be regenerated.

Gibbering Fiend

When this creature enters, it deals 1 damage to each opponent.
Delirium — At the beginning of each opponent's upkeep, if there are four or more card types among cards in your graveyard, this creature deals 1 damage to that player.

Dreadfeast Demon

Flying
At the beginning of your end step, sacrifice a non-Demon creature. If you do, create a token that's a copy of this creature.

Vrock

Flying
Toxic Spores — At the beginning of your end step, if a permanent you controlled left the battlefield this turn, each opponent loses 3 life.

Daggerclaw Imp

Valgavoth, Terror Eater

Flying, lifelink
Ward—Sacrifice three nonland permanents.
If a card you didn't control would be put into an opponent's graveyard from anywhere, exile it instead.
During your turn, you may play cards exiled with Valgavoth. If you cast a spell this way, pay life equal to its mana value rather than pay its mana cost.

Archfiend of Spite

Flying
Whenever a source an opponent controls deals damage to this creature, that source's controller loses that much life unless they sacrifice that many permanents of their choice.
Madness {3}{B}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Doomsday Excruciator

Flying
When this creature enters, if it was cast, each player exiles all but the bottom six cards of their library face down.
At the beginning of your upkeep, draw a card.

Sire of Insanity

At the beginning of each end step, each player discards their hand.

Impetuous Devils

Trample, haste
When this creature attacks, up to one target creature defending player controls blocks it this combat if able.
At the beginning of the end step, sacrifice this creature.

Plague Drone

Flying
Rot Fly — If an opponent would gain life, that player loses that much life instead.

Soot Imp

Flying
Whenever a player casts a nonblack spell, that player loses 1 life.

Demon of Death's Gate

You may pay 6 life and sacrifice three black creatures rather than pay this spell's mana cost.
Flying, trample

Hellrider

Haste
Whenever a creature you control attacks, this creature deals 1 damage to the player or planeswalker it's attacking.

Frenzied Devils

Haste
Whenever you cast a noncreature spell, this creature gets +2/+2 until end of turn.

Demon's Jester

Flying
Hellbent — This creature gets +2/+1 as long as you have no cards in hand.

Reign of the Pit

Each player sacrifices a creature of their choice. Create an X/X black Demon creature token with flying, where X is the total power of the creatures sacrificed this way.

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.

Hollowborn Barghest

At the beginning of your upkeep, if you have no cards in hand, each opponent loses 2 life.
At the beginning of each opponent's upkeep, if that player has no cards in hand, they lose 2 life.

Embodiment of Agonies

Flying, deathtouch
This creature enters with a +1/+1 counter on it for each different mana cost among nonland cards in your graveyard. (For example, {2}{B} and {1}{B}{B} are different mana costs.)

Fiendish Duo

First strike (This creature deals combat damage before creatures without first strike.)
If a source would deal damage to an opponent, it deals double that damage to that player instead.

Lord of the Forsaken

Flying, trample
{B}, Sacrifice another creature: Target player mills three cards.
Pay 1 life: Add {C}. Spend this mana only to cast a spell from your graveyard.

Archfiend of Despair

Flying
Your opponents can't gain life.
At the beginning of each end step, each opponent loses life equal to the life that player lost this turn. (Damage causes loss of life.)