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

Whenever another permanent enters the battlefield under your control, each opponent mills a card.

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

Spells and abilities your opponents control can't cause their controller to search their library.

-1: Target player mills four cards. Then exile each opponent's graveyard.

+1: Create a 2/3 blue and black Nightmare creature token with "Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library."

-3: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.

-7: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.

+2: Exile the top three cards of target opponent's library.

-X: Put a creature card with mana value X exiled with Ashiok, Nightmare Weaver onto the battlefield under your control. That creature is a Nightmare in addition to its other types.

-10: Exile all cards from all opponents' hands and graveyards.

Equipped creature has myriad. (Whenever it attacks, for each opponent other than defending player, you may create a token that's a copy of that creature that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)

Equip {4}

Bojuka Bog enters the battlefield tapped.

When Bojuka Bog enters the battlefield, exile target player's graveyard.

{T}: Add {B}.

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

Create a 1/1 blue and black Horror creature token with flying.

Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Whenever you cast a blue spell, exile the top card of target player's library.

Whenever you cast a black spell, exile the top card of target player's library.

Your opponents can't cast spells with the same name as a card exiled with Circu, Dimir Lobotomist.

{T}: Add {U}.

{T}: Add {B}.

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

At the beginning of your end step, you may exile target creature you control, then return that card to the battlefield under your control.

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.

When Court of Cunning enters the battlefield, 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.)

{1}, {T}: Exile target card from a graveyard.

{1}, Exile Crook of Condemnation: Exile all graveyards.

Add {B}{B}{B}.

Counter target creature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Counter target creature or enchantment spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may shuffle up to four target cards from your graveyard into your library.

Dimir Aqueduct enters the battlefield tapped.

When Dimir Aqueduct enters the battlefield, return a land you control to its owner's hand.

{T}: Add {U}{B}.

Dismal Backwater enters the battlefield tapped.

When Dismal Backwater enters the battlefield, you gain 1 life.

{T}: Add {U} or {B}.

Exile up to two target creatures you control, then return those cards to the battlefield under their owner's control.

Drowned Catacomb enters the battlefield tapped unless you control an Island or a Swamp.

{T}: Add {U} or {B}.

Menace

Whenever Elder Brain attacks a player, exile all cards from that player's hand, then they draw that many cards. You may play lands and cast spells from among the exiled 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.

Exile target creature you control, then return that card to the battlefield under its owner's control. If it's a Spirit, put a +1/+1 counter on it.

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

{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.

When Faceless Butcher enters the battlefield, exile target creature other than Faceless Butcher.

When Faceless Butcher leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Each opponent mills fourteen cards.

Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

When you cycle Fractured Sanity, each opponent mills four cards.

Exile two target artifacts, creatures, and/or lands you control, then return those cards to the battlefield under your control.

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.

{T}: Add one mana of any color.

{2}, {T}: Exile target card from a graveyard.

({T}: Add {U} or {B}.)

Ice Tunnel enters the battlefield tapped.

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

When Lantern of the Lost enters the battlefield, exile target card from a graveyard.

{1}, {T}, Exile Lantern of the Lost: Exile all cards from all graveyards, then draw a card.

If Leyline of the Void is in your opening hand, you may begin the game with it on the battlefield.

If a card would be put into an opponent's graveyard from anywhere, exile it instead.

Kicker {3}{U}

Each opponent mills eight cards. If this spell was kicked, instead each opponent mills half their library, rounded up.

Manascape Refractor enters the battlefield tapped.

Manascape Refractor has all activated abilities of all lands on the battlefield.

You may spend mana as though it were mana of any color to pay the activation costs of Manascape Refractor's abilities.

Whenever an opponent casts a spell, that player mills two cards.

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.

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.

Flying

Whenever Mirko Vosk, Mind Drinker deals combat damage to a player, that player reveals cards from the top of their library until they reveal four land cards, then puts those cards into their graveyard.

Whenever Nemesis of Reason attacks, defending player mills ten cards.

Flying

Whenever another nontoken creature you control dies, you may exile it. If you do, create a token that's a copy of that creature, except it's 1/1 and it's a Nightmare in addition to its other types.

If an artifact or creature entering the battlefield causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Path of Ancestry enters the battlefield 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.)

Counter target spell unless its controller discards their hand.

Transmute {1}{U}{B} ({1}{U}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Indestructible

As long as your devotion to blue and black is less than seven, Phenax isn't a creature.

Creatures you control have "{T}: Target player mills X cards, where X is this creature's toughness."

When Phyrexian Rager enters the battlefield, you draw a card and you lose 1 life.

Pit of Offerings enters the battlefield tapped.

When Pit of Offerings enters the battlefield, exile up to three target cards from graveyards.

{T}: Add {C}.

{T}: Add one mana of any of the exiled cards' colors.

Whenever another card is put into a graveyard from anywhere, exile that card.

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Whenever you draw a card, each opponent mills two cards.

Create a token that's a copy of target creature you control, except it isn't legendary.

Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)

When Ravenous Chupacabra enters the battlefield, destroy target creature an opponent controls.

As Reflections of Littjara enters the battlefield, choose a creature type.

Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

Restless Reef enters the battlefield tapped.

{T}: Add {U} or {B}.

{2}{U}{B}: Until end of turn, Restless Reef becomes a 4/4 blue and black Shark creature with deathtouch. It's still a land.

Whenever Restless Reef attacks, target player mills four cards.

Ward {2}

As Roaming Throne enters the battlefield, choose a creature type.

Roaming Throne 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.

Landfall -- Whenever a land enters the battlefield under your control, each opponent mills three cards. (To mill a card, a player puts the top card of their library into their graveyard.)

Imprint -- When Semblance Anvil enters the battlefield, you may exile a nonland card from your hand.

Spells you cast that share a card type with the exiled card cost {2} less to cast.

Shipwreck Marsh enters the battlefield tapped unless you control two or more other lands.

{T}: Add {U} or {B}.

Whenever Sludge Monster enters the battlefield 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.

{T}: Add {C}{C}.

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

Target opponent mills thirteen cards.

{3}{U}{U}: Put Startled Awake from your graveyard onto the battlefield transformed. Activate only as a sorcery.

Skulk (This creature can't be blocked by creatures with greater power.)

When Persistent Nightmare deals combat damage to a player, return it to its owner's hand.

({T}: Add {U} or {B}.)

Sunken Hollow enters the battlefield tapped unless you control two or more basic lands.

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

Equipped creature gets +2/+2 and has protection from green and from white.

Whenever equipped creature deals combat damage to a player, exile up to one target creature you own, then search your library for a basic land card. Put both cards onto the battlefield under your control, then shuffle.

Equip {2}

Counter target spell unless its controller pays {X}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

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

{T}, Sacrifice Terramorphic Expanse: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Indestructible

As long as your devotion to blue is less than five, Thassa isn't a creature.

At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.

{3}{U}: Tap another target creature.

At the beginning of each end step, put a slime counter on each creature you don't control.

Creatures you don't control get -1/-1 for each slime counter on them.

Whenever a creature you don't control with a slime counter on it dies, create a 1/1 black Slug creature token.

{U}{B}, Sacrifice a Slug: Draw a card.

Whenever equipped creature attacks, defending player reveals cards from the top of their library until they reveal a land card. The creature gets +1/+0 until end of turn for each card revealed this way. That player puts the revealed cards into their graveyard.

Equip {2}

Umbris, Fear Manifest gets +1/+1 for each card your opponents own in exile.

Whenever Umbris or another Nightmare or Horror enters the battlefield under your control, target opponent exiles cards from the top of their library until they exile a land card.

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

Cleave {1}{U}{U} (You may cast this spell for its cleave cost. If you do, remove the words in square brackets.)

Counter target spell [that wasn't cast from its owner's hand].

Skulk (This creature can't be blocked by creatures with greater power.)

Whenever Wharf Infiltrator 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.

Flying

When Wormfang Drake enters the battlefield, sacrifice it unless you exile a creature you control other than Wormfang Drake.

When Wormfang Drake leaves the battlefield, return the exiled card to the battlefield under its owner's control.

When Yarok's Fenlurker enters the battlefield, each opponent exiles a card from their hand.

{2}{B}: Yarok's Fenlurker gets +1/+1 until end of turn.

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.)