Garza's Assassin

Sacrifice Garza's Assassin: Destroy target nonblack creature.
Recover—Pay half your life, rounded up. (When another creature is put into your graveyard from the battlefield, you may pay half your life, rounded up. If you do, return this card from your graveyard to your hand. Otherwise, exile this card.)

Imp's Mischief

Change the target of target spell with a single target. You lose life equal to that spell's mana value.

Enlightened Tutor

Search your library for an artifact or enchantment card, reveal it, then shuffle and put that card on top.

Dark Confidant

At the beginning of your upkeep, reveal the top card of your library and put that card into your hand. You lose life equal to its mana value.

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.)

Marshland Bloodcaster

Flying
{1}{B}, {T}: Rather than pay the mana cost of the next spell you cast this turn, you may pay life equal to that spell's mana value.

Lotho, Corrupt Shirriff

Whenever a player casts their second spell each turn, you lose 1 life and create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Diabolic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Reanimate

Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its mana value.

Bolas's Citadel

You may look at the top card of your library any time.
You may play lands and cast spells from the top of your library. If you cast a spell this way, pay life equal to its mana value rather than pay its mana cost.
{T}, Sacrifice ten nonland permanents: Each opponent loses 10 life.

Axis of Mortality

At the beginning of your upkeep, you may have two target players exchange life totals.

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.

Magus of the Mirror

{T}, Sacrifice Magus of the Mirror: Exchange life totals with target opponent. Activate only during your upkeep.

Phyrexian Unlife

You don't lose the game for having 0 or less life.
As long as you have 0 or less life, all damage is dealt to you as though its source had infect. (Damage is dealt to you in the form of poison counters.)

Xander's Pact

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell.)
Each opponent exiles the top card of their library. You may cast spells from among those cards this turn. If you cast a spell this way, pay life equal to that spell's mana value rather than pay its mana cost.

Cruel Bargain

Draw four cards. You lose half your life, rounded up.

Plains

Idyllic Tutor

Search your library for an enchantment card, reveal it, put it into your hand, then shuffle.

Lurking Evil

Pay half your life, rounded up: Lurking Evil becomes a 4/4 Phyrexian Horror creature with flying.

Devour in Shadow

Destroy target creature. It can't be regenerated. You lose life equal to that creature's toughness.

Reverse the Sands

Redistribute any number of players' life totals. (Each of those players gets one life total back.)

Evra, Halcyon Witness

Lifelink
{4}: Exchange your life total with Evra, Halcyon Witness's power.

Dark Tutelage

Swamp

Demonic Tutor

Dire Tactics

Exile target creature. If you don't control a Human, you lose life equal to that creature's toughness.

The Golden Throne

Arcane Life-support — If you would lose the game, instead exile The Golden Throne and your life total becomes 1.
A Thousand Souls Die Every Day — {T}, Sacrifice a creature: Add three mana in any combination of colors.

Grim Tutor

Search your library for a card, put that card into your hand, then shuffle. You lose 3 life.

Stunning Reversal

The next time you would lose the game this turn, instead draw seven cards and your life total becomes 1.
Exile Stunning Reversal.

Repay in Kind

Each player's life total becomes the lowest life total among all players.

Vendetta

Destroy target nonblack creature. It can't be regenerated. You lose life equal to that creature's toughness.

Profane Transfusion

Two target players exchange life totals. You create an X/X colorless Horror artifact creature token, where X is the difference between those players' life totals.

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Soul Conduit

{6}, {T}: Two target players exchange life totals.

Cruel Tutor

Pain Seer

Inspired — Whenever Pain Seer becomes untapped, reveal the top card of your library and put that card into your hand. You lose life equal to that card's mana value.