Unspeakable Symbol

Pay 3 life: Put a +1/+1 counter on target creature.

Wall of Blood

Defender (This creature can't attack.)
Pay 1 life: This creature gets +1/+1 until end of turn.

Nightmare Lash

Equipped creature gets +1/+1 for each Swamp you control.
Equip—Pay 3 life. (Pay 3 life: Attach to target creature you control. Equip only as a sorcery.)

Necropotence

Skip your draw step.
Whenever you discard a card, exile that card from your graveyard.
Pay 1 life: Exile the top card of your library face down. Put that card into your hand at the beginning of your next end step.

Shadowcloak Vampire

Pay 2 life: This creature gains flying until end of turn. (It can't be blocked except by creatures with flying or reach.)

Koh, the Face Stealer

When Koh enters, exile up to one other target creature.
Whenever another nontoken creature dies, you may exile it.
Pay 1 life: Choose a creature card exiled with Koh.
Koh has all activated and triggered abilities of the last chosen card.

Ethereal Champion

Pay 1 life: Prevent the next 1 damage that would be dealt to this creature this turn.

Magus of the Mirror

{T}, Sacrifice this creature: Exchange life totals with target opponent. Activate only during your upkeep.

Mister Negative

Vigilance, lifelink
Darkforce Inversion — When Mister Negative enters, you may exchange life totals with target opponent. If you lost life this way, draw that many cards.

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.

Glorifier of Dusk

Pay 2 life: This creature gains flying until end of turn.
Pay 2 life: This creature gains vigilance until end of turn.

Marrow Bats

Flying
Pay 4 life: Regenerate this creature.

Deepwood Ghoul

Axis of Mortality

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

Adanto Vanguard

As long as this creature is attacking, it gets +2/+0.
Pay 4 life: This creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Martyrs' Tomb

Pay 2 life: Prevent the next 1 damage that would be dealt to target creature this turn.

Mischievous Poltergeist

Flying
Pay 1 life: Regenerate this creature.

Doom Whisperer

Flying, trample
Pay 2 life: Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Reverse the Sands

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

Repay in Kind

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

Kuro, Pitlord

At the beginning of your upkeep, sacrifice Kuro unless you pay {B}{B}{B}{B}.
Pay 1 life: Target creature gets -1/-1 until end of turn.

Carrion Howler

Pay 1 life: This creature gets +2/-1 until end of turn.

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.

Souldrinker

Pay 3 life: Put a +1/+1 counter on this creature.

Soul Conduit

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

Selenia, Dark Angel

Flying
Pay 2 life: Return Selenia to its owner's hand.

Crovax, Ascendant Hero

Other white creatures get +1/+1.
Nonwhite creatures get -1/-1.
Pay 2 life: Return Crovax to its owner's hand.

Soul Channeling

Enchant creature
Pay 2 life: Regenerate enchanted creature.

Arco-Flagellant

Squad {2} (As an additional cost to cast this spell, you may pay {2} any number of times. When this creature enters, create that many tokens that are copies of it.)
This creature can't block.
Endurant — Pay 3 life: This creature gains indestructible until end of turn.

Phyrexian Colossus

This creature doesn't untap during your untap step.
Pay 8 life: Untap this creature.
This creature can't be blocked except by three or more creatures.