Ob Nixilis, Captive Kingpin

Flying, trample
Whenever one or more opponents each lose exactly 1 life, put a +1/+1 counter on Ob Nixilis, Captive Kingpin. Exile the top card of your library. Until your next end step, you may play that card.

Nightshade Harvester

Whenever a land an opponent controls enters, that player loses 1 life. Put a +1/+1 counter on Nightshade Harvester.

Revenge of Ravens

Whenever a creature attacks you or a planeswalker you control, that creature's controller loses 1 life and you gain 1 life.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

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.

Hellrider

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

Zulaport Cutthroat

Whenever Zulaport Cutthroat or another creature you control dies, each opponent loses 1 life and you gain 1 life.

Bastion of Remembrance

When Bastion of Remembrance enters, create a 1/1 white Human Soldier creature token.
Whenever a creature you control dies, each opponent loses 1 life and you gain 1 life.

Goblin Bombardment

Sacrifice a creature: Goblin Bombardment deals 1 damage to any target.

Ob Nixilis, the Hate-Twisted

Whenever an opponent draws a card, Ob Nixilis, the Hate-Twisted deals 1 damage to that player.
−2: Destroy target creature. Its controller draws two cards.

Battle Strain

Whenever a creature blocks, Battle Strain deals 1 damage to that creature's controller.

Retreat to Hagra

Landfall — Whenever a land you control enters, choose one —
• Target creature gets +1/+0 and gains deathtouch until end of turn.
• Each opponent loses 1 life and you gain 1 life.

Ashnod's Altar

Phyrexian Arena

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

Bedevil

Destroy target artifact, creature, or planeswalker.

All Will Be One

Whenever you put one or more counters on a permanent or player, All Will Be One deals that much damage to target opponent, creature an opponent controls, or planeswalker an opponent controls.

Viscera Seer

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

Mana Geyser

Add {R} for each tapped land your opponents control.

Stormfist Crusader

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

Blood Artist

Whenever Blood Artist or another creature dies, target player loses 1 life and you gain 1 life.

Gimli, Counter of Kills

Trample
Whenever a creature an opponent controls dies, Gimli, Counter of Kills deals 1 damage to that creature's controller.

Sokenzan, Crucible of Defiance

{T}: Add {R}.
Channel — {3}{R}, Discard Sokenzan, Crucible of Defiance: Create two 1/1 colorless Spirit creature tokens. They gain haste until end of turn. This ability costs {1} less to activate for each legendary creature you 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.)

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, Rampaging Ferocidon deals 1 damage to that creature's controller.

The Meathook Massacre

When The Meathook Massacre enters, each creature gets -X/-X until end of turn.
Whenever a creature you control dies, each opponent loses 1 life.
Whenever a creature an opponent controls dies, you gain 1 life.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

Skullclamp

Equipped creature gets +1/-1.
Whenever equipped creature dies, draw two cards.
Equip {1}

Kardur, Doomscourge

When Kardur, Doomscourge 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.

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.