Have

Psionic Ritual

Replicate—Tap an untapped Horror you control. (When you cast this spell, copy it for each time you paid its replicate cost. You may choose new targets for the copies.)
Exile target instant or sorcery card from a graveyard and copy it. You may cast the copy without paying its mana cost.
Exile Psionic Ritual.

Shipwreck Marsh

This land enters tapped unless you control two or more other lands.
{T}: Add {U} or {B}.

Day of Black Sun

Each creature with mana value X or less loses all abilities until end of turn. Destroy those creatures.

Agadeem, the Undercrypt

As this land enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {B}.

Agadeem's Awakening

Return from your graveyard to the battlefield any number of target creature cards that each have a different mana value X or less.

Agadeem's Awakening // Agadeem, the Undercrypt

Creeping Tar Pit

This land enters tapped.
{T}: Add {U} or {B}.
{1}{U}{B}: Until end of turn, this land becomes a 3/2 blue and black Elemental creature. It's still a land. It can't be blocked this turn.

Espers to Magicite

Exile each opponent's graveyard. When you do, choose up to one target creature card exiled this way. Create a token that's a copy of that card, except it's an artifact and it loses all other card types.

Island

Choked Estuary

As this land enters, you may reveal an Island or Swamp card from your hand. If you don't, this land enters tapped.
{T}: Add {U} or {B}.

Sunken Hollow

({T}: Add {U} or {B}.)
This land enters tapped unless you control two or more basic lands.

The True Scriptures

(As this Saga enters and after your draw step, add a lore counter.)
I — For each opponent, destroy up to one target creature or planeswalker that player controls.
II — Each opponent discards three cards, then mills three cards.
III — Put all creature cards from all graveyards onto the battlefield under your control. Exile this Saga, then return it to the battlefield (front face up).

Sheoldred

Menace
When Sheoldred enters, each opponent sacrifices a nontoken creature or planeswalker of their choice.
{4}{B}: Exile Sheoldred, then return it to the battlefield transformed under its owner's control. Activate only as a sorcery and only if an opponent has eight or more cards in their graveyard.

Sheoldred // The True Scriptures

Outrageous Robbery

Target opponent exiles the top X cards of their library face down. You may look at and play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any type to cast it.

River of Tears

{T}: Add {U}. If you played a land this turn, add {B} instead.

Vashta Nerada

Indestructible
Shadow (This creature can block or be blocked by only creatures with shadow.)
Morbid — At the beginning of each end step, if a creature died this turn, put a +1/+1 counter on this creature.

Riverchurn Monument

{1}, {T}: Any number of target players each mill two cards. (Each of them puts the top two cards of their library into their graveyard.)
Exhaust — {2}{U}{U}, {T}: Any number of target players each mill cards equal to the number of cards in their graveyard. (Activate each exhaust ability only once.)

Swamp

Cadaver Lab

When you unlock this door, return target creature card from your graveyard to your hand.
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Defiled Crypt

Whenever one or more cards leave your graveyard, create a 2/2 black Horror enchantment creature token. This ability triggers only once each turn.
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Defiled Crypt // Cadaver Lab

Fraying Sanity

Enchant player
At the beginning of each end step, enchanted player mills X cards, where X is the number of cards put into their graveyard from anywhere this turn.

Overture

Target opponent mills half their library, rounded down. (Then exile this card. You may play the land later from exile.)

Jidoor, Aristocratic Capital

Jidoor, Aristocratic Capital // Overture

Temple of Deceit

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 {U} or {B}.

Intellect Devourer

Devour Intellect — When this creature enters, each opponent exiles a card from their hand until this creature leaves the battlefield.
Body Thief — You may play lands and cast spells from among cards exiled with this creature. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.

Mind Grind

Each opponent reveals cards from the top of their library until they reveal X land cards, then puts all cards revealed this way into their graveyard. X can't be 0.

Dimir Signet

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.)

Altar of the Brood

Whenever another permanent you control enters, each opponent mills a card.

Tainted Isle

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

Impostor Syndrome

Whenever a nontoken creature you control deals combat damage to a player, create a token that's a copy of it, except it isn't legendary.

Zellix, Sanity Flayer

Hive Mind — Whenever a player mills one or more creature cards, you create a 1/1 black Horror creature token.
{1}, {T}: Target player mills three cards.
Choose a Background (You can have a Background as a second commander.)

Tasha's Hideous Laughter

Each opponent exiles cards from the top of their library until that player has exiled cards with total mana value 20 or greater.

Sunken Ruins

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

Nephalia Drownyard

{T}: Add {C}.
{1}{U}{B}, {T}: Target player mills three cards.

Command Tower

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

Umbris, Fear Manifest

Umbris gets +1/+1 for each card your opponents own in exile.
Whenever Umbris or another Nightmare or Horror you control enters, target opponent exiles cards from the top of their library until they exile a land card.

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. This artifact deals 1 damage to you.

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Susur Secundi, Void Altar

This land enters tapped.
{T}: Add {B}.
Station (Tap another creature you control: Put charge counters equal to its power on this Planet. Station only as a sorcery.)
12+ | {1}{B}, {T}, Pay 2 life, Sacrifice a creature: Draw cards equal to the sacrificed creature's power. Activate only as a sorcery.

Darkwater Catacombs

The Water Crystal

Blue spells you cast cost {1} less to cast.
If an opponent would mill one or more cards, they mill that many cards plus four instead.
{4}{U}{U}, {T}: Each opponent mills cards equal to the number of cards in your hand.

Aboleth Spawn

Flash
Ward {2}
Probing Telepathy — Whenever a creature entering under an opponent's control causes a triggered ability of that creature to trigger, you may copy that ability. You may choose new targets for the copy.

Increasing Confusion

Target player mills X cards. If this spell was cast from a graveyard, that player mills twice that many cards instead.
Flashback {X}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Ahriman

Flying, deathtouch
{3}, Sacrifice another creature or artifact: Draw a card.

Wharf Infiltrator

Skulk (This creature can't be blocked by creatures with greater power.)
Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card.
Whenever you discard a creature card, you may pay {2}. If you do, create a 3/2 colorless Eldrazi Horror creature token.

Bojuka Bog

This land enters tapped.
When this land enters, exile target player's graveyard.
{T}: Add {B}.

Drowned Catacomb

This land enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)

Herald's Horn

As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Spellskite

{U/P}: Change a target of target spell or ability to this creature. ({U/P} can be paid with either {U} or 2 life.)

Silent Hallcreeper

This creature can't be blocked.
Whenever this creature deals combat damage to a player, choose one that hasn't been chosen —
• Put two +1/+1 counters on this creature.
• Draw a card.
• This creature becomes a copy of another target creature you control.

Watery Grave

({T}: Add {U} or {B}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Roaming Throne

Ward {2}
As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
If a triggered ability of another creature you control of the chosen type triggers, it triggers an additional time.

Consuming Aberration

Consuming Aberration's power and toughness are each equal to the number of cards in your opponents' graveyards.
Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

Fractured Realm

If a triggered ability of a permanent you control triggers, that ability triggers an additional time.
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Mirror Room

When you unlock this door, create a token that's a copy of target creature you control, except it's a Reflection in addition to its other creature types.
(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)

Mirror Room // Fractured Realm

Court of Cunning

When this enchantment enters, you become the monarch.
At the beginning of your upkeep, any number of target players each mill two cards. If you're the monarch, each of those players mills ten cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

Cabal Coffers

{2}, {T}: Add {B} for each Swamp you control.

Blue Mage's Cane

Job select
Equipped creature gets +0/+2, is a Wizard in addition to its other types, and has "Whenever this creature attacks, exile up to one target instant or sorcery card from defending player's graveyard. If you do, copy it. You may cast the copy by paying {3} rather than paying its mana cost."
Spirit of the Whalaqee — Equip {2}

Shambling Cie'th

This creature enters tapped.
Whenever you cast a noncreature spell, you may pay {B}. If you do, return this card from your graveyard to your hand.

Singularity Rupture

Destroy all creatures, then any number of target players each mill half their library, rounded down.

Mind Funeral

Target opponent reveals cards from the top of their library until four land cards are revealed. That player puts all cards revealed this way into their graveyard.

Brainstealer Dragon

Flying
At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.
Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.

Captain N'ghathrod

Horrors you control have menace.
Whenever a Horror you control deals combat damage to a player, that player mills that many cards.
At the beginning of your end step, choose target artifact or creature card in an opponent's graveyard that was put there from their library this turn. Put it onto the battlefield under your control.

Grisly Spectacle

Destroy target nonartifact creature. Its controller mills cards equal to that creature's power.

Grell Philosopher

Aberrant Tinkering — When this creature enters and at the beginning of your upkeep, each Horror you control gains all activated abilities of target artifact an opponent controls until end of turn. You may spend blue mana as though it were mana of any color to activate those abilities.

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Siphon Insight

Look at the top two cards of target opponent's library. Exile one of them face down and put the other on the bottom of that library. You may play the exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell.
Flashback {1}{U}{B}

Rogue's Passage

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

Kindred Discovery

As this enchantment enters, choose a creature type.
Whenever a creature you control of the chosen type enters or attacks, draw a card.

Archive Trap

If an opponent searched their library this turn, you may pay {0} rather than pay this spell's mana cost.
Target opponent mills thirteen cards.

Mind Flayer

Dominate Monster — When this creature enters, gain control of target creature for as long as you control this creature.

White Lotus Tile

This artifact enters tapped.
{T}: Add X mana of any one color, where X is the greatest number of creatures you control that have a creature type in common.

Urza's Incubator

As this artifact enters, choose a creature type.
Creature spells of the chosen type cost {2} less to cast.

Glimpse the Unthinkable

The Darkness Crystal

Black spells you cast cost {1} less to cast.
If a nontoken creature an opponent controls would die, instead exile it and you gain 2 life.
{4}{B}{B}, {T}: Put target creature card exiled with The Darkness Crystal onto the battlefield tapped under your control with two additional +1/+1 counters on it.

Cyclonic Rift

Return target nonland permanent you don't control to its owner's hand.
Overload {6}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Fractured Sanity

Each opponent mills fourteen cards.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle this card, each opponent mills four cards.

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Ash Barrens

{T}: Add {C}.
Basic landcycling {1} ({1}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

Endless Evil

Enchant creature you control
At the beginning of your upkeep, create a token that's a copy of enchanted creature, except the token is 1/1.
When enchanted creature dies, if that creature was a Horror, return this card to its owner's hand.

Uchuulon

Uchuulon's power is equal to the number of Crabs, Oozes, and/or Horrors you control.
Horrific Symbiosis — At the beginning of your end step, exile up to one target creature card from an opponent's graveyard. If you do, create a token that's a copy of this creature.

Phyrexian Obliterator

Trample
Whenever a source deals damage to this creature, that source's controller sacrifices that many permanents of their choice.

Soporific Springs

As this land enters, you may pay 3 life. If you don't, it enters tapped.
{T}: Add {U}.

Sink into Stupor

Return target spell or nonland permanent an opponent controls to its owner's hand.

Sink into Stupor // Soporific Springs

Gloomlake Verge

{T}: Add {U}.
{T}: Add {B}. Activate only if you control an Island or a Swamp.

Defiler of Flesh

Menace
As an additional cost to cast black permanent spells, you may pay 2 life. Those spells cost {B} less to cast if you paid life this way. This effect reduces only the amount of black mana you pay.
Whenever you cast a black permanent spell, target creature you control gets +1/+1 and gains menace until end of turn.

Bruvac the Grandiloquent

If an opponent would mill one or more cards, they mill twice that many cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

Overlord of the Floodpits

Impending 4—{1}{U}{U} (If you cast this spell for its impending cost, it enters with four time counters and isn't a creature until the last is removed. At the beginning of your end step, remove a time counter from it.)
Flying
Whenever this permanent enters or attacks, draw two cards, then discard a card.

Arcane Signet

Maddening Cacophony

Kicker {3}{U}
Each opponent mills eight cards. If this spell was kicked, instead each opponent mills half their library, rounded up.

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.

The Final Days

Create two tapped 2/2 black Horror creature tokens. If this spell was cast from a graveyard, instead create X of those tokens, where X is the number of creature cards in your graveyard.
Flashback {4}{B}{B} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Grazilaxx, Illithid Scholar

Whenever a creature you control becomes blocked, you may return it to its owner's hand.
Whenever one or more creatures you control deal combat damage to a player, draw a card.

Drownyard Temple

{T}: Add {C}.
{3}: Return this card from your graveyard to the battlefield tapped.

Sol Ring

Altar of Dementia

Sacrifice a creature: Target player mills cards equal to the sacrificed creature's power.

Sludge Monster

Whenever this creature enters or attacks, put a slime counter on up to one other target creature.
Non-Horror creatures with slime counters on them lose all abilities and have base power and toughness 2/2.