Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

You may have Phantasmal Image enter the battlefield as a copy of any creature on the battlefield, except it's an Illusion in addition to its other types and it has "When this creature becomes the target of a spell or ability, sacrifice it."

Flash Ward {2} Probing Telepathy — Whenever a creature entering the battlefield 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.

You may have Imposter Mech enter the battlefield as a copy of a creature an opponent controls, except it's a Vehicle artifact with crew 3 and it loses all other card types. Crew 3

Counter target instant or sorcery spell unless its controller pays {1}. Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

If it's not your turn, you may exile a blue card from your hand rather than pay this spell's mana cost. Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost. Counter target spell.

({U/P} can be paid with either {U} or 2 life.) Counter target spell with mana value 1.

If an opponent cast three or more spells this turn, you may pay {0} rather than pay this spell's mana cost. Exile any number of target spells.

Counter target spell. At the beginning of your next upkeep, pay {3}{U}{U}. If you don't, you lose the game.

You may have Flesh Duplicate enter the battlefield as a copy of any creature on the battlefield, except it has vanishing 3 if that creature doesn't have vanishing. (A permanent with vanishing 3 enters the battlefield with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)

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.

Whenever a creature you control deals combat damage to a player, you may draw a card. {1}{U}, {T}: Creatures your opponents control attack this turn if able.

Islandwalk (This creature can't be blocked as long as defending player controls an Island.) Whenever Cold-Eyed Selkie deals combat damage to a player, you may draw that many cards.

You may look at the top card of your library any time. You may cast Merfolk spells from the top of your library. Whenever you cast a Merfolk spell, you may pay {1}. If you do, create a 1/1 blue Merfolk creature token.

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Whenever equipped creature deals combat damage to a player, you draw that many cards. Equip {4} Equip Shaman, Warlock, or Wizard {1}

Whenever a Merfolk you control deals combat damage to a player, draw a card.

Svyelun of Sea and Sky has indestructible as long as you control at least two other Merfolk. Whenever Svyelun attacks, draw a card. Other Merfolk you control have ward {1}. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

When Thassa's Oracle enters the battlefield, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Indestructible When The One Ring enters the battlefield, if you cast it, you gain protection from everything until your next turn. At the beginning of your upkeep, you lose 1 life for each burden counter on The One Ring. {T}: Put a burden counter on The One Ring, then draw a card for each burden counter on The One Ring.

{4}: Scry 1, then reveal the top card of your library. If it's a land card, put it onto the battlefield tapped. Otherwise, draw a card. Partner (You can have two commanders if both have partner.)

{T}: Add {C}{C}. Ancient Tomb deals 2 damage to you.

{T}: Add {G}. Channel — {1}{G}, Discard Boseiju, Who Endures: Destroy target artifact, enchantment, or nonbasic land an opponent controls. That player may search their library for a land card with a basic land type, put it onto the battlefield, then shuffle. This ability costs {1} less to activate for each legendary creature you control.

({T}: Add {G} or {U}.) As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

As Cavern of Souls enters the battlefield, 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.

{T}: Add {U}. Cephalid Coliseum deals 1 damage to you. Threshold — {U}, {T}, Sacrifice Cephalid Coliseum: Target player draws three cards, then discards three cards. Activate only if seven or more cards are in your graveyard.

Whenever City of Brass becomes tapped, it deals 1 damage to you. {T}: Add one mana of any color.

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

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

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

{T}, Pay 1 life, Sacrifice Flooded Strand: Search your library for a Plains or Island card, put it onto the battlefield, then shuffle.

{T}: Add {G} for each creature you control.

If Gemstone Caverns is in your opening hand and you're not the starting player, you may begin the game with Gemstone Caverns on the battlefield with a luck counter on it. If you do, exile a card from your hand. {T}: Add {C}. If Gemstone Caverns has a luck counter on it, instead add one mana of any color.

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

{T}: Add {U}. {U}, {T}: Untap target legendary permanent.

{T}, Pay 1 life, Sacrifice Misty Rainforest: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

{T}: Add {C}. {2}, {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

{T}: Add {U}. Channel — {3}{U}, Discard Otawara, Soaring City: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

{T}, Pay 1 life, Sacrifice Polluted Delta: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Rejuvenating Springs enters the battlefield tapped unless you have two or more opponents. {T}: Add {G} or {U}.

{T}, Pay 1 life, Sacrifice Scalding Tarn: Search your library for an Island or Mountain card, put it onto the battlefield, then shuffle.

({T}: Add {G}.)

({T}: Add {U}.)

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

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

{T}, Pay 1 life: Add {G} or {U}. {1}, {T}, Sacrifice Waterlogged Grove: Draw a card.

{T}, Pay 1 life, Sacrifice Windswept Heath: Search your library for a Forest or Plains card, put it onto the battlefield, then shuffle.

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

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

Flying {T}: Add one mana of any color.

Imprint — When Chrome Mox enters the battlefield, you may exile a nonartifact, nonland card from your hand. {T}: Add one mana of any of the exiled card's colors.

You may have Copy Artifact enter the battlefield as a copy of any artifact on the battlefield, except it's an enchantment in addition to its other types.

As an additional cost to cast this spell, sacrifice a land. Search your library for a land card, put that card onto the battlefield, then shuffle.

Creatures you control have "{T}: Add one mana of any color."

Tap an untapped creature you control: Untap target basic land.

Exile Elvish Spirit Guide from your hand: Add {G}.

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

Grim Monolith doesn't untap during your untap step. {T}: Add {C}{C}{C}. {4}: Untap Grim Monolith.

{T}, Sacrifice Jeweled Lotus: Add three mana of any one color. Spend this mana only to cast your commander.

Whenever you tap a nonland permanent for mana, add one mana of any type that permanent produced. {5}{G}{U}: Look at the top five cards of your library. You may put a non-Human creature card from among them onto the battlefield. Put the rest on the bottom of your library in a random order.

{T}: Untap another target permanent.

{T}, Sacrifice Lotus Petal: Add one mana of any color.

At the beginning of your upkeep, flip a coin. If you lose the flip, Mana Crypt deals 3 damage to you. {T}: Add {C}{C}.

Mana Vault doesn't untap during your untap step. At the beginning of your upkeep, you may pay {4}. If you do, untap Mana Vault. At the beginning of your draw step, if Mana Vault is tapped, it deals 1 damage to you. {T}: Add {C}{C}{C}.

{T}: Add one mana of any color among legendary creatures and planeswalkers you control.

If Mox Diamond would enter the battlefield, you may discard a land card instead. If you do, put Mox Diamond onto the battlefield. If you don't, put it into its owner's graveyard. {T}: Add one mana of any color.

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Untap all permanents you control during each other player's untap step.

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

Islandwalk (This creature can't be blocked as long as defending player controls an Island.) Merfolk spells and Wizard spells you cast cost {1} less to cast.

As an additional cost to cast this spell, sacrifice a blue permanent. Counter target spell.

Sacrifice Cursecatcher: Counter target instant or sorcery spell unless its controller pays {1}.

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.")

If you control a commander, you may cast this spell without paying its mana cost. Counter target noncreature spell.

Return all noncreature, nonland permanents to their owners' hands.

Flash This spell can't be countered. Whenever you cast a spell, choose up to one — • Return target spell you don't control to its owner's hand. • Return target nonland permanent to its owner's hand.

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token. Tap seven untapped Merfolk you control: Counter target spell.

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Flash When Merfolk Trickster enters the battlefield, tap target creature an opponent controls. It loses all abilities until end of turn.

Sacrifice Mistcaller: Until end of turn, if a nontoken creature would enter the battlefield and it wasn't cast, exile it instead.

+2: Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this artifact: You gain 3 life.") +1: Target artifact or creature loses all abilities and becomes a green Elk creature with base power and toughness 3/3. −5: Exchange control of target artifact or creature you control and target creature an opponent controls with power 3 or less.

Exile target artifact or creature. Its controller creates a 4/4 blue and red Elemental creature token.

Flash Flying When Subtlety enters the battlefield, choose up to one target creature spell or planeswalker spell. Its owner puts it on the top or bottom of their library. Evoke—Exile a blue card from your hand.

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.) Flying When Thieving Skydiver enters the battlefield, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to Thieving Skydiver.

Search target opponent's library for a creature card and put that card onto the battlefield under your control. Then that player shuffles.

Whenever you cast a Merfolk spell, create a 1/1 blue Merfolk creature token with hexproof. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

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.) Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle.

As an additional cost to cast this spell, sacrifice a creature. Search your library for a creature card with mana value X or less, where X is 2 plus the sacrificed creature's mana value. Put that card onto the battlefield, then shuffle. Exile Eldritch Evolution.

Search your library and/or graveyard for a creature card with mana value X or less and put it onto the battlefield. If you search your library this way, shuffle. If X is 10 or more, creatures you control get +X/+X and gain haste until end of turn.

Search your library for a green creature card with mana value X or less, put it onto the battlefield, then shuffle. Shuffle Green Sun's Zenith into its owner's library.

Search your library for an instant or sorcery card, reveal it, then shuffle and put that card on top.

As an additional cost to cast this spell, sacrifice a creature. Search your library for a creature card with mana value equal to 1 plus the sacrificed creature's mana value, put that card onto the battlefield with an additional +1/+1 counter on it, then shuffle.

{3}, {T}: Search your library for a Merfolk permanent card, put it onto the battlefield, then shuffle.

When Spellseeker enters the battlefield, you may search your library for an instant or sorcery card with mana value 2 or less, reveal it, put it into your hand, then shuffle.

{G}, Discard a creature card: Search your library for a creature card, reveal that card, put it into your hand, then shuffle.

Creatures don't untap during their controllers' untap steps. Whenever a creature enters the battlefield, untap all creatures.

At the beginning of your end step, untap all Merfolk you control.

You may spend mana as though it were mana of any color to activate abilities of creatures you control. Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron. {T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

At the beginning of each of your main phases, if you haven't added mana with this ability this turn, you may add X mana of any one color, where X is the number of Islands target opponent controls.