Dusk Mangler

As an additional cost to cast this spell, sacrifice a creature, discard a card, or pay 4 life.
When this creature enters, each opponent sacrifices a creature of their choice, discards a card, and loses 4 life.

Gray Merchant of Asphodel

When this creature enters, 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.)

Fraying Omnipotence

Each player loses half their life, then discards half the cards in their hand, then sacrifices half the creatures they control of their choice. Round up each time.

Blood Tithe

Each opponent loses 3 life. You gain life equal to the life lost this way.

Court of Ambition

When this enchantment enters, you become the monarch.
At the beginning of your upkeep, each opponent loses 3 life unless they discard a card. If you're the monarch, instead each opponent loses 6 life unless they discard two cards.

Zoyowa Lava-Tongue

Deathtouch
At the beginning of your end step, if you descended this turn, each opponent may discard a card or sacrifice a permanent of their choice. Zoyowa deals 3 damage to each opponent who didn't. (You descended if a permanent card was put into your graveyard from anywhere.)

Forsaken Wastes

Players can't gain life.
At the beginning of each player's upkeep, that player loses 1 life.
Whenever this enchantment becomes the target of a spell, that spell's controller loses 5 life.

Bloodchief Ascension

At the beginning of each end step, if an opponent lost 2 or more life this turn, you may put a quest counter on this enchantment. (Damage causes loss of life.)
Whenever a card is put into an opponent's graveyard from anywhere, if this enchantment has three or more quest counters on it, you may have that player lose 2 life. If you do, you gain 2 life.

Dire Fleet Ravager

Menace, deathtouch
When this creature enters, each player loses a third of their life, rounded up.

Ribbons

Aftermath (Cast this spell only from your graveyard. Then exile it.)
Each opponent loses X life.

Cut // Ribbons

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.)

Loyal Subordinate

Menace (This creature can't be blocked except by two or more creatures.)
Lieutenant — At the beginning of combat on your turn, if you control your commander, each opponent loses 3 life.

Great Unclean One

Reverberating Summons — At the beginning of your end step, each opponent loses 2 life. Then for each opponent who has less life than you, create a 1/3 black Demon creature token named Plaguebearer of Nurgle.

Dark Suspicions

At the beginning of each opponent's upkeep, that player loses X life, where X is the number of cards in that player's hand minus the number of cards in your hand.

Havoc Festival

Players can't gain life.
At the beginning of each player's upkeep, that player loses half their life, rounded up.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Bond of Agony

As an additional cost to cast this spell, pay X life.
Each other player loses X life.