Modern Horizon 2 spoilers have kicked off, and among all the high-profile reprints and exciting re-imagining of old favorites is a new staple-to-be: Rishadan Dockhand.

Rishadan Dockhand brings Rishadan Port effect to Modern, and Merfolk are going to take advantage of it as another disruptive tool for a tribe that relies on them. In Legacy, Merfolk decks use Wasteland to slow the opponent's mana development while it beats down—Rishadan Dockhand will give opponents a taste of this in Modern.

Rishadan Dockhand feels like an upgrade to Cursecatcher, which just doesn't do anything against a lot of the field. Rishadan Dockhand can slow down spells of all sorts, potentially even acting like a Time Walk effect by denying the opponent a meaningful play. Tapping things like Tron lands and bounce lands, or even color-hosing an opponent, sounds great to me. It also doesn't require any sacrifice, and can help kill the opponent after it's done disrupting them. It's going to be fun, that's for sure, and I can't wait to see how it plays out.

As just a normal rare in a set that's going to be opened a lot for its fetchlands and other chase cards, Rishadan Dockhand should be pretty cheap to come by eventually, and a welcome addition to a Modern Merfolk deck on any budget. While we wait for the set to release next month, there's plenty of other effective one-drop options for putting together a Merfolk deck under $100.

Basic Budget Merfolk

Magic: The Gathering TCG Deck - Basic Budget Merfolk by Adam Yurchick

'Basic Budget Merfolk' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: Adam Yurchick

Event:

Rank:

Modern

Market Price: $136.94

Cards

Benthic Biomancer

Color Identity:U

Market Price: $0.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/183198_200w.jpg

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

Buy This Card! https://shop.tcgplayer.com/magic/ravnica-allegiance/benthic-biomancer

Tormod's Crypt

Market Price: $0.23

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215346_200w.jpg

{T}, Sacrifice Tormod's Crypt: Exile all cards from target player's graveyard.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/tormods-crypt

Master of Waves

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149164_200w.jpg

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters the battlefield, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-waves

Silvergill Adept

Color Identity:U

Market Price: $0.22

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/155592_200w.jpg

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters the battlefield, draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/rivals-of-ixalan/silvergill-adept

Lord of Atlantis

Color Identity:U

Market Price: $17.98

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/14613_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/timeshifted/lord-of-atlantis

Merfolk Trickster

Color Identity:U

Market Price: $0.82

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162225_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/dominaria/merfolk-trickster

Master of the Pearl Trident

Color Identity:U

Market Price: $2.30

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149154_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-the-pearl-trident

Spell Pierce

Color Identity:U

Market Price: $0.29

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145258_200w.jpg

Counter target noncreature spell unless its controller pays {2}.

Buy This Card! https://shop.tcgplayer.com/magic/ixalan/spell-pierce

Spreading Seas

Color Identity:U

Market Price: $0.68

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/33438_200w.jpg

Enchant land
When Spreading Seas enters the battlefield, draw a card.
Enchanted land is an Island.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar/spreading-seas

Dismember

Color Identity:B

Market Price: $2.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/98390_200w.jpg

({B/P} can be paid with either {B} or 2 life.)
Target creature gets -5/-5 until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2015/dismember

Island

Color Identity:U

Market Price: $0.05

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/196475_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/commander-2019/island-291

Cursecatcher

Color Identity:U

Market Price: $0.43

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/161420_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/masters-25/cursecatcher

Deprive

Color Identity:U

Market Price: $1.39

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/34753_200w.jpg

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

Buy This Card! https://shop.tcgplayer.com/magic/rise-of-the-eldrazi/deprive

Aether Gust

Color Identity:U

Market Price: $0.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192535_200w.jpg

Choose target spell or permanent that's red or green. Its owner puts it on the top or bottom of their library.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2020/aether-gust

Harbinger of the Tides

Color Identity:U

Market Price: $0.45

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149153_200w.jpg

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/harbinger-of-the-tides

Merfolk is about as straight-forward as they come in terms of tribal decks, and Magic decks in general. It's accordingly consistent, fast, and effective. Its plan is simple: deploy as many Merfolk as it can as quickly as possible, pump them with the +1/+1 effect on its lord creatures, and overwhelm the opponent. A dash of disruption, both Dismember as removal and Spell Pierce as a counterspell, and all of the sideboard cards help stop whatever the opponent is doing.

As a one-color deck, color and mana problems in general are mostly nonexistent. The curve is low, so it only needs a few lands to operate. It's fast and aggressive, so it aims to win the game before it goes long and flooding becomes an issue. It does have access to some card draw with Silvergill Adept, and the filtering of Benthic Biomancer. Master of Waves is also a sort of card advantage, and if not immediately destroyed, will easily win most games.

The sideboard offers nothing but more disruption to better tailor the deck for its opponent—be it with more counterspells, creature removal, or speciality disruption. Note that Spreading Seas does double duty—not only hosing lands, but also making them an Island to enable islandwalk given by the lords. It can be a big deal against a deck like Jund or Death's Shadow, where the three-color mana could be exploited, and they have big walls like Tarmogoyf.

Building it Up

Merfolk can be built quite cheaply and will do plenty of winning, but there are a handful of potential high-impact upgrades—each that will help elevate the deck to a new level.

Built-Up Budget Merfolk

Magic: The Gathering TCG Deck - Built-Up Budget Merfolk by Adam Yurchick

'Built-Up Budget Merfolk' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: Adam Yurchick

Event:

Rank:

Modern

Market Price: $221.36

Cards

Spell Pierce

Color Identity:U

Market Price: $0.29

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145258_200w.jpg

Counter target noncreature spell unless its controller pays {2}.

Buy This Card! https://shop.tcgplayer.com/magic/ixalan/spell-pierce

Aether Gust

Color Identity:U

Market Price: $0.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192535_200w.jpg

Choose target spell or permanent that's red or green. Its owner puts it on the top or bottom of their library.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2020/aether-gust

Harbinger of the Tides

Color Identity:U

Market Price: $0.45

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149153_200w.jpg

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/harbinger-of-the-tides

Mutavault

Market Price: $9.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/69900_200w.jpg

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Buy This Card! https://shop.tcgplayer.com/magic/magic-2014-m14/mutavault

Relic of Progenitus

Market Price: $4.61

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/118645_200w.jpg

{T}: Target player exiles a card from their graveyard.
{1}, Exile Relic of Progenitus: Exile all cards from all graveyards. Draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/eternal-masters/relic-of-progenitus

Silvergill Adept

Color Identity:U

Market Price: $0.22

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/155592_200w.jpg

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters the battlefield, draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/rivals-of-ixalan/silvergill-adept

Spreading Seas

Color Identity:U

Market Price: $0.68

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/33438_200w.jpg

Enchant land
When Spreading Seas enters the battlefield, draw a card.
Enchanted land is an Island.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar/spreading-seas

Benthic Biomancer

Color Identity:U

Market Price: $0.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/183198_200w.jpg

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

Buy This Card! https://shop.tcgplayer.com/magic/ravnica-allegiance/benthic-biomancer

Phantasmal Image

Color Identity:U

Market Price: $15.99

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/128595_200w.jpg

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."

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2017/phantasmal-image

Master of Waves

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149164_200w.jpg

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters the battlefield, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-waves

Dismember

Color Identity:B

Market Price: $2.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/98390_200w.jpg

({B/P} can be paid with either {B} or 2 life.)
Target creature gets -5/-5 until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2015/dismember

Merfolk Trickster

Color Identity:U

Market Price: $0.82

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162225_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/dominaria/merfolk-trickster

Cursecatcher

Color Identity:U

Market Price: $0.43

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/161420_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/masters-25/cursecatcher

Master of the Pearl Trident

Color Identity:U

Market Price: $2.30

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149154_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-the-pearl-trident

Deprive

Color Identity:U

Market Price: $1.39

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/34753_200w.jpg

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

Buy This Card! https://shop.tcgplayer.com/magic/rise-of-the-eldrazi/deprive

Lord of Atlantis

Color Identity:U

Market Price: $17.98

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/14613_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/timeshifted/lord-of-atlantis

Island

Color Identity:U

Market Price: $0.05

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/196475_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/commander-2019/island-291

Upgrade: Mutavault

Merfolk are synonymous with Mutavault, and historically no tribe has made better use of the changeling land. In a deck full of lords, the 2/2 is usually larger, and the extra offense it adds makes the deck that much more potent.

It's not just that Mutavault makes the deck denser with action. Mutavault acts like a haste creature if it's already in play, so in some games it brings the damage output to a level impossible without it.

It's a truly irreplaceable and invaluable card, and my highest priority when upgrading the Merfolk deck.

Upgrade: Phantasmal Image

Once Mutavault is acquired, I'd start looking at Phantasmal Image. It's not a Merfolk, but it can copy any of them—whether it be Silvergill Adept to draw a card, a lord to get aggressive, something else, or even the opponent's creature. It offers a bit of flexibility in a deck without much of it, and its versatility and power make it worth the price tag.

Upgrade: Relic of Progenitus

In the sideboard, Relic of Progenitus does a better job than Tormod's Crypt. The card advantage and flexibility make it a better option against things like Snapcaster Mage or Tarmogoyf, and it's just a superior card in general when speed isn't the biggest issue. If not already available, it's also a card well-worth its price.

Taking Things to the Next Level

The biggest step in bringing Merfolk up from budget-level to its truly full-power and competitive level is adding Aether Vial. A staple of countless creature decks in Modern and Legacy, Aether Vial isn't cheap, but it's among the single best investments one can make in terms of opening access to more decks.

Basic Merfolk

Magic: The Gathering TCG Deck - Basic Merfolk by Adam Yurchick

'Basic Merfolk' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: Adam Yurchick

Event:

Rank:

Modern

Market Price: $442.50

Cards

Phantasmal Image

Color Identity:U

Market Price: $15.99

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/128595_200w.jpg

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."

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2017/phantasmal-image

Aether Vial

Market Price: $55.62

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145333_200w.jpg

At the beginning of your upkeep, you may put a charge counter on Aether Vial.
{T}: You may put a creature card with mana value equal to the number of charge counters on Aether Vial from your hand onto the battlefield.

Buy This Card! https://shop.tcgplayer.com/magic/iconic-masters/aether-vial

Relic of Progenitus

Market Price: $4.61

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/118645_200w.jpg

{T}: Target player exiles a card from their graveyard.
{1}, Exile Relic of Progenitus: Exile all cards from all graveyards. Draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/eternal-masters/relic-of-progenitus

Lord of Atlantis

Color Identity:U

Market Price: $17.98

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/14613_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/timeshifted/lord-of-atlantis

Spell Pierce

Color Identity:U

Market Price: $0.29

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145258_200w.jpg

Counter target noncreature spell unless its controller pays {2}.

Buy This Card! https://shop.tcgplayer.com/magic/ixalan/spell-pierce

Spreading Seas

Color Identity:U

Market Price: $0.68

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/33438_200w.jpg

Enchant land
When Spreading Seas enters the battlefield, draw a card.
Enchanted land is an Island.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar/spreading-seas

Dismember

Color Identity:B

Market Price: $2.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/98390_200w.jpg

({B/P} can be paid with either {B} or 2 life.)
Target creature gets -5/-5 until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2015/dismember

Benthic Biomancer

Color Identity:U

Market Price: $0.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/183198_200w.jpg

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

Buy This Card! https://shop.tcgplayer.com/magic/ravnica-allegiance/benthic-biomancer

Harbinger of the Tides

Color Identity:U

Market Price: $0.45

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149153_200w.jpg

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/harbinger-of-the-tides

Island

Color Identity:U

Market Price: $0.05

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/196475_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/commander-2019/island-291

Master of the Pearl Trident

Color Identity:U

Market Price: $2.30

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149154_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-the-pearl-trident

Silvergill Adept

Color Identity:U

Market Price: $0.22

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/155592_200w.jpg

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters the battlefield, draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/rivals-of-ixalan/silvergill-adept

Mutavault

Market Price: $9.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/69900_200w.jpg

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Buy This Card! https://shop.tcgplayer.com/magic/magic-2014-m14/mutavault

Merfolk Trickster

Color Identity:U

Market Price: $0.82

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162225_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/dominaria/merfolk-trickster

Deprive

Color Identity:U

Market Price: $1.39

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/34753_200w.jpg

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

Buy This Card! https://shop.tcgplayer.com/magic/rise-of-the-eldrazi/deprive

Master of Waves

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149164_200w.jpg

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters the battlefield, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-waves

Aether Gust

Color Identity:U

Market Price: $0.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192535_200w.jpg

Choose target spell or permanent that's red or green. Its owner puts it on the top or bottom of their library.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2020/aether-gust

Upgrade: Aether Vial

Aether Vial is a mana ramp engine for creatures, and the speed this provides lets Merfolk overwhelm the opponent. Freeing up mana is especially valuable in a deck that has other things to do with it—whether it's keeping it up for counterspells, spending it on removal, or to activate Mutavault, Benthic Biomancer, or Rishadan Dockhand. None of which will be as effective without Aether Vial helping.

Aether Vial also helps hose counterspells. Not a small factor in a format with lots of them, and many, many more coming with Counterspell soon arriving in Modern Horizons 2.

Building on an Unlimited Budget

With no budget concern, there are some high dollar additions that add a bit of spice to the deck. Here's a full-powered list that's been winning on MTGO and inspired my budget builds.

Magic: The Gathering TCG Deck - Merfolk by Enigma01

'Merfolk' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: Enigma01

Event:

Rank:

Modern

Market Price: $830.73

Cards

Mutavault

Market Price: $9.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/69900_200w.jpg

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Buy This Card! https://shop.tcgplayer.com/magic/magic-2014-m14/mutavault

Island

Color Identity:U

Market Price: $0.05

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/196475_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/commander-2019/island-291

Master of Waves

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149164_200w.jpg

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters the battlefield, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/master-of-waves

Dismember

Color Identity:B

Market Price: $2.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/98390_200w.jpg

({B/P} can be paid with either {B} or 2 life.)
Target creature gets -5/-5 until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/modern-masters-2015/dismember

Harbinger of the Tides

Color Identity:U

Market Price: $0.45

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149153_200w.jpg

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Buy This Card! https://shop.tcgplayer.com/magic/duel-decks-merfolk-vs-goblins/harbinger-of-the-tides

Force of Negation

Color Identity:U

Market Price: $81.03

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/190647_200w.jpg

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.

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Master of the Pearl Trident

Color Identity:U

Market Price: $2.30

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/149154_200w.jpg

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

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Mystic Reflection

Color Identity:U

Market Price: $3.13

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230497_200w.jpg

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter the battlefield this turn, they enter as copies of the chosen creature.
Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

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Relic of Progenitus

Market Price: $4.61

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/118645_200w.jpg

{T}: Target player exiles a card from their graveyard.
{1}, Exile Relic of Progenitus: Exile all cards from all graveyards. Draw a card.

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Merfolk Trickster

Color Identity:U

Market Price: $0.82

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162225_200w.jpg

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

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Oboro, Palace in the Clouds

Color Identity:U

Market Price: $69.93

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/12500_200w.jpg

{T}: Add {U}.
{1}: Return Oboro, Palace in the Clouds to its owner's hand.

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Phantasmal Image

Color Identity:U

Market Price: $15.99

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/128595_200w.jpg

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."

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Spell Pierce

Color Identity:U

Market Price: $0.29

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145258_200w.jpg

Counter target noncreature spell unless its controller pays {2}.

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Deprive

Color Identity:U

Market Price: $1.39

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/34753_200w.jpg

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

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Cavern of Souls

Market Price: $77.80

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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.

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Silvergill Adept

Color Identity:U

Market Price: $0.22

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As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters the battlefield, draw a card.

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Lord of Atlantis

Color Identity:U

Market Price: $17.98

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/14613_200w.jpg

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

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Benthic Biomancer

Color Identity:U

Market Price: $0.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/183198_200w.jpg

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

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Aether Vial

Market Price: $55.62

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145333_200w.jpg

At the beginning of your upkeep, you may put a charge counter on Aether Vial.
{T}: You may put a creature card with mana value equal to the number of charge counters on Aether Vial from your hand onto the battlefield.

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Spreading Seas

Color Identity:U

Market Price: $0.68

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/33438_200w.jpg

Enchant land
When Spreading Seas enters the battlefield, draw a card.
Enchanted land is an Island.

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Upgrade: Cavern of Souls

If you want to hose counterspells even more, turn to Cavern of Souls. It's not a pure upgrade without a downside. It can't help with blue mana towards counterspells and such, but the deck can support a couple to push through threats. This would be my lowest priority upgrade, but it's not a bad card to include.

Upgrade: Force of Negation

Another possible upgrade for Merfolk is Force of Negation. It's not a necessary piece of the puzzle, but it's a great counterspell option. Not all lists use it, but many do. And at the very least, having a couple in the 75 is probably a good idea.

Upgrade: Oboro, Palace in the Clouds

It's also worth mentioning Oboro, Palace in the Clouds. In terms of impact versus cost, it's hard to imagine less added value per dollar spent, but it's played for a reason. For one, it can be returned to fuel the discard of Benthic Biomancer—no small thing in topdeck situations. Two, for the cost of a land drop it can turn colorless mana into blue, so it fixes problems that Mutavault could cause.

The Water is Warm

When Modern Horizons 2 hits, I'm definitely adding a set of Rishadan Dockhand over Benthic Biomancer and seeing how the extra disruption plays out. Restricting mana will make Spell Pierce better, but I'm excited to just jam a playset of Counterspell in the maindeck. Merfolk definitely got some gifts, and there may even be more in the set. So it's going to be better than ever. The beauty of building a classic tribal deck is that inevitably more great cards will keep coming in the future.