Children of Korlis

Sacrifice Children of Korlis: You gain life equal to the life you've lost this turn. (Damage causes loss of life.)

Staff of Compleation

{T}, Pay 1 life: Destroy target permanent you own.
{T}, Pay 2 life: Add one mana of any color.
{T}, Pay 3 life: Proliferate.
{T}, Pay 4 life: Draw a card.
{5}: Untap Staff of Compleation.

Sorin, Ravenous Neonate

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
+2: Create a Food token.
−1: Sorin, Ravenous Neonate deals damage equal to the amount of life you gained this turn to any target.
−6: Gain control of target creature. It becomes a Vampire in addition to its other types. Put a lifelink counter on it if you control a white permanent other than that creature or Sorin.

Sorin of House Markov

Lifelink
Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
At the beginning of your postcombat main phase, if you gained 3 or more life this turn, exile Sorin of House Markov, then return him to the battlefield transformed under his owner's control.

Sorin of House Markov // Sorin, Ravenous Neonate

Axis of Mortality

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

Wall of Blood

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

Boggart Bog

As Boggart Bog enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {B}.

Boggart Trawler

When Boggart Trawler enters the battlefield, exile target player's graveyard.

Boggart Trawler // Boggart Bog

Razorgrass Field

As Razorgrass Field enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {W}.

Razorgrass Ambush

Razorgrass Ambush deals 3 damage to target attacking or blocking creature.

Razorgrass Ambush // Razorgrass Field

Underworld Connections

Enchant land
Enchanted land has "{T}, Pay 1 life: Draw a card."

Myr Convert

Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
{T}, Pay 2 life: Add one mana of any color.

Exsanguinate

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

Reverse the Sands

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

Adanto Vanguard

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

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.

Temple of Aclazotz

(Transforms from Arguel's Blood Fast.)
{T}: Add {B}.
{T}, Sacrifice a creature: You gain life equal to the sacrificed creature's toughness.

Arguel's Blood Fast

{1}{B}, Pay 2 life: Draw a card.
At the beginning of your upkeep, if you have 5 or less life, you may transform Arguel's Blood Fast.

Arguel's Blood Fast // Temple of Aclazotz

Magus of the Mirror

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

Resolute Archangel

Flying
When Resolute Archangel enters the battlefield, if your life total is less than your starting life total, it becomes equal to your starting life total.

Toxic Deluge

As an additional cost to cast this spell, pay X life.
All creatures get -X/-X until end of turn.

Amalia Benavides Aguirre

Ward—Pay 3 life.
Whenever you gain life, Amalia Benavides Aguirre explores. Then destroy all other creatures if its power is exactly 20. (To have this creature explore, reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Debt to the Deathless

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

Killing Wave

For each creature, its controller sacrifices it unless they pay X life.

Vesper Ghoul

{T}, Pay 1 life: Add one mana of any color.

Font of Agonies

Whenever you pay life, put that many blood counters on Font of Agonies.
{1}{B}, Remove four blood counters from Font of Agonies: Destroy target creature.

Treasure Dredger

{1}, {T}, Pay 1 life: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Soul Conduit

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

Tainted Sigil

{T}, Sacrifice Tainted Sigil: You gain life equal to the total life lost by all players this turn. (Damage causes loss of life.)

Bond of Agony

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