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.

Getting

Ancient Cellarspawn

Each spell you cast that's a Demon, Horror, or Nightmare costs {1} less to cast.
Whenever you cast a spell, if the amount of mana spent to cast it was less than its mana value, target opponent loses life equal to the difference.

Erebos's Intervention

Choose one —
• Target creature gets -X/-X until end of turn. You gain X life.
• Exile up to twice X target cards from graveyards.

Bloodstained Mire

{T}, Pay 1 life, Sacrifice Bloodstained Mire: Search your library for a Swamp or Mountain card, put it onto the battlefield, then shuffle.

Soul Channeling

Enchant creature
Pay 2 life: Regenerate enchanted creature.

Jaya's Immolating Inferno

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Jaya's Immolating Inferno deals X damage to each of up to three targets.

Plunge into Darkness

Choose one —
• Sacrifice any number of creatures. You gain 3 life for each creature sacrificed this way.
• Pay any amount of life, then look at that many cards from the top of your library. Put one of those cards into your hand and exile the rest.
Entwine {B} (Choose both if you pay the entwine cost.)

Heartless Hidetsugu

{T}: Heartless Hidetsugu deals damage to each player equal to half that player's life total, rounded down.

Have

Darkstar Augur

Offspring {B} (You may pay an additional {B} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Flying
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.

Twinflame Tyrant

Flying
If a source you control would deal damage to an opponent or a permanent an opponent controls, it deals double that damage instead.

Judith, Carnage Connoisseur

Whenever you cast an instant or sorcery spell, choose one —
• That spell gains deathtouch and lifelink.
• Create a 2/2 red Imp creature token with "When this creature dies, it deals 2 damage to each opponent."

City on Fire

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
If a source you control would deal damage to a permanent or player, it deals triple that damage instead.

Tentative Connection

This spell costs {3} less to cast if you control a creature with menace.
Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn.

Commune with Lava

Exile the top X cards of your library. Until the end of your next turn, you may play those cards.

Fake Your Own Death

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control and you create a Treasure token." (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Return the Past

During your turn, each instant and sorcery card in your graveyard has flashback. Its flashback cost is equal to its mana cost.

Insatiable Avarice

Spree (Choose one or more additional costs.)
+ {2} — Search your library for a card, then shuffle and put that card on top.
+ {B}{B} — Target player draws three cards and loses 3 life.

Blackcleave Cliffs

Blackcleave Cliffs enters tapped unless you control two or fewer other lands.
{T}: Add {B} or {R}.

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.

Storm King's Thunder

When you next cast an instant or sorcery spell this turn, copy that spell X times. You may choose new targets for the copies.

Unspeakable Symbol

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

Flare of Duplication

You may sacrifice a nontoken red creature rather than pay this spell's mana cost.
Copy target instant or sorcery spell. You may choose new targets for the copy.

Immolating Souleater

{R/P}: Immolating Souleater gets +1/+0 until end of turn. ({R/P} can be paid with either {R} or 2 life.)

Thousand-Year Elixir

You may activate abilities of creatures you control as though those creatures had haste.
{1}, {T}: Untap target creature.

Comet Storm

Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.)
Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.

Slaughter Pact

Destroy target nonblack creature.
At the beginning of your next upkeep, pay {2}{B}. If you don't, you lose the game.

Magus of the Mirror

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

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.

March of Wretched Sorrow

As an additional cost to cast this spell, you may exile any number of black cards from your hand. This spell costs {2} less to cast for each card exiled this way.
March of Wretched Sorrow deals X damage to target creature or planeswalker and you gain X life.

Wall of Blood

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

Deadly Cover-Up

As an additional cost to cast this spell, you may collect evidence 6.
Destroy all creatures. If evidence was collected, exile a card from an opponent's graveyard. Then search its owner's graveyard, hand, and library for any number of cards with that name and exile them. That player shuffles, then draws a card for each card exiled from their hand this way.

Devil's Play

Devil's Play deals X damage to any target.
Flashback {X}{R}{R}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Treasonous Ogre

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Pay 3 life: Add {R}.

Tainted Peak

{T}: Add {C}.
{T}: Add {B} or {R}. Activate only if you control a Swamp.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Restless Vents

Restless Vents enters tapped.
{T}: Add {B} or {R}.
{1}{B}{R}: Until end of turn, Restless Vents becomes a 2/3 black and red Insect creature with menace. It's still a land.
Whenever Restless Vents attacks, you may discard a card. If you do, draw a card.

Rowan, Scion of War

Menace
{T}: Spells you cast this turn that are black and/or red cost {X} less to cast, where X is the amount of life you lost this turn. Activate only as a sorcery.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Command Tower

Temple of Malice

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {B} or {R}.

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.)

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Moltensteel Dragon

({R/P} can be paid with either {R} or 2 life.)
Flying
{R/P}: Moltensteel Dragon gets +1/+0 until end of turn.

Swamp

Cavern of Souls

As Cavern of Souls enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.

Not Dead After All

Until end of turn, target creature you control gains "When this creature dies, return it to the battlefield tapped under its owner's control, then create a Wicked Role token attached to it." (Enchanted creature gets +1/+1. When this Aura is put into a graveyard, each opponent loses 1 life.)

Sulfurous Springs

{T}: Add {C}.
{T}: Add {B} or {R}. Sulfurous Springs deals 1 damage to you.

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.

Solphim, Mayhem Dominus

If a source you control would deal noncombat damage to an opponent or a permanent an opponent controls, it deals double that damage to that player or permanent instead.
{1}{R/P}{R/P}, Discard two cards: Put an indestructible counter on Solphim, Mayhem Dominus. ({R/P} can be paid with either {R} or 2 life.)

Smoldering Marsh

({T}: Add {B} or {R}.)
Smoldering Marsh enters tapped unless you control two or more basic lands.

Bloodletter of Aclazotz

Flying
If an opponent would lose life during your turn, they lose twice that much life instead. (Damage causes loss of life.)

Crackle with Power

Crackle with Power deals five times X damage to each of up to X targets.

Pact Weapon

As long as Pact Weapon is attached to a creature, you don't lose the game for having 0 or less life.
Whenever equipped creature attacks, draw a card and reveal it. The creature gets +X/+X until end of turn and you lose X life, where X is that card's mana value.
Equip—Discard a card.

Marvin, Murderous Mimic

Marvin, Murderous Mimic has all activated abilities of creatures you control that don't have the same name as this creature.

Mischievous Poltergeist

Flying
Pay 1 life: Regenerate Mischievous Poltergeist.

Repay in Kind

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

Fabled Passage

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then if you control four or more lands, untap that land.

Black Market Connections

At the beginning of your first main phase, choose one or more —
• Sell Contraband — Create a Treasure token. You lose 1 life.
• Buy Information — Draw a card. You lose 2 life.
• Hire a Mercenary — Create a 3/2 colorless Shapeshifter creature token with changeling. You lose 3 life. (It has every creature type.)

Shadowblood Ridge

Apex of Power

Exile the top seven cards of your library. Until end of turn, you may cast spells from among them.
If this spell was cast from your hand, add ten mana of any one color.

Exsanguinate

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

Talisman of Indulgence

{T}: Add {C}.
{T}: Add {B} or {R}. Talisman of Indulgence deals 1 damage to you.

Rakdos Signet

Graven Cairns

{T}: Add {C}.
{B/R}, {T}: Add {B}{B}, {B}{R}, or {R}{R}.

Blood Celebrant

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

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.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Fiery Emancipation

If a source you control would deal damage to a permanent or player, it deals triple that damage to that permanent or player instead.

Banefire

Banefire deals X damage to any target.
If X is 5 or more, this spell can't be countered and the damage can't be prevented.

Exotic Orchard

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.)

Mountain

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.

Foreboding Ruins

As Foreboding Ruins enters, you may reveal a Swamp or Mountain card from your hand. If you don't, Foreboding Ruins enters tapped.
{T}: Add {B} or {R}.

Wound Reflection

At the beginning of each end step, each opponent loses life equal to the life they lost this turn. (Damage causes loss of life.)

Dragonskull Summit

Dragonskull Summit enters tapped unless you control a Swamp or a Mountain.
{T}: Add {B} or {R}.

Sol Ring

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)