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.

Sower of Discord

Flying
As this creature enters, choose two players.
Whenever damage is dealt to one of the chosen players, the other chosen player also loses that much life.

Overseer of the Damned

Flying
When this creature enters, you may destroy target creature.
Whenever a nontoken creature an opponent controls dies, create a tapped 2/2 black Zombie creature token.

Rune-Scarred Demon

Flying
When this creature enters, search your library for a card, put it into your hand, then shuffle.

Rakdos, Patron of Chaos

Flying, trample
At the beginning of your end step, target opponent may sacrifice two nonland, nontoken permanents of their choice. If they don't, you draw two cards.

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.

Spawn of Mayhem

Spectacle {1}{B}{B} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
Flying, trample
At the beginning of your upkeep, this creature deals 1 damage to each player. Then if you have 10 or less life, put a +1/+1 counter on this creature.

Lord of Change

Flying, ward {3}
Architect of Deception — When this creature enters, draw three cards.

Grinning Demon

At the beginning of your upkeep, you lose 2 life.
Morph {2}{B}{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.)

The Speed Demon

Flying, trample
Start your engines! (If you have no speed, it starts at 1. It increases once on each of your turns when an opponent loses life. Max speed is 4.)
At the beginning of your end step, you draw X cards and lose X life, where X is your speed.

Demon of Catastrophes

As an additional cost to cast this spell, sacrifice a creature.
Flying, trample

Bloodgift Demon

Flying
At the beginning of your upkeep, target player draws a card and loses 1 life.

Bringer of the Last Gift

Flying
When this creature enters, if you cast it, each player sacrifices all other creatures they control. Then each player returns all creature cards from their graveyard that weren't put there this way to the battlefield.

Abyssal Persecutor

Flying, trample
You can't win the game and your opponents can't lose the game.

Demon of Dark Schemes

Flying
When this creature enters, all other creatures get -2/-2 until end of turn.
Whenever another creature dies, you get {E} (an energy counter).
{2}{B}, Pay {E}{E}{E}{E}: Put target creature card from a graveyard onto the battlefield under your control tapped.

Archfiend of the Dross

Flying
This creature enters with four oil counters on it.
At the beginning of your upkeep, remove an oil counter from this creature. Then if it has no oil counters on it, you lose the game.
Whenever a creature an opponent controls dies, its controller loses 2 life.

Reaper from the Abyss

Flying
Morbid — At the beginning of each end step, if a creature died this turn, destroy target non-Demon creature.

Demon of Wailing Agonies

Flying
Lieutenant — As long as you control your commander, this creature gets +2/+2 and has "Whenever this creature deals combat damage to a player, that player sacrifices a creature of their choice."

Balor

Flying
Whenever this creature attacks or dies, choose one or more. Each mode must target a different player.
• Target opponent draws three cards, then discards three cards at random.
• Target opponent sacrifices a nontoken artifact of their choice.
• This creature deals damage to target opponent equal to the number of cards in their hand.

Orcus, Prince of Undeath

Flying, trample
When Orcus enters, choose one —
• Each other creature gets -X/-X until end of turn. You lose X life.
• Return up to X target creature cards with total mana value X or less from your graveyard to the battlefield. They gain haste until end of turn.

Be'lakor, the Dark Master

Flying
Prince of Chaos — When Be'lakor, the Dark Master enters, you draw X cards and you lose X life, where X is the number of Demons you control.
Lord of Torment — Whenever another Demon you control enters, it deals damage equal to its power to any target.

Vilis, Broker of Blood

Flying
{B}, Pay 2 life: Target creature gets -1/-1 until end of turn.
Whenever you lose life, draw that many cards. (Damage causes loss of life.)

Kardur, Doomscourge

When Kardur enters, until your next turn, creatures your opponents control attack each combat if able and attack a player other than you if able.
Whenever an attacking creature dies, each opponent loses 1 life and you gain 1 life.