Have

Spined Megalodon

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever Spined Megalodon attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Prime Speaker Zegana

Prime Speaker Zegana enters the battlefield with X +1/+1 counters on it, where X is the greatest power among other creatures you control.
When Prime Speaker Zegana enters the battlefield, draw cards equal to its power.

Tangletrap

Choose one —
• Tangletrap deals 5 damage to target creature with flying.
• Destroy target artifact.

Jadecraft Artisan

When Jadecraft Artisan enters the battlefield, target creature gets +2/+2 until end of turn.

Triton Fortune Hunter

Heroic — Whenever you cast a spell that targets Triton Fortune Hunter, draw a card.

Dragon Turtle

Flash
Drag Below — When Dragon Turtle enters the battlefield, tap it and up to one target creature an opponent controls. They don't untap during their controllers' next untap steps.

Headwater Sentries

Skyclave Squid

Defender
Landfall — Whenever a land enters the battlefield under your control, Skyclave Squid can attack this turn as though it didn't have defender.

Shaper Apprentice

Shaper Apprentice has flying as long as you control another Merfolk.

Sky-Eel School

Flying
When Sky-Eel School enters the battlefield, draw a card, then discard a card.

Triton Waverider

Constellation — Whenever an enchantment enters the battlefield under your control, Triton Waverider gains flying until end of turn.

Watertrap Weaver

When Watertrap Weaver enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Gray Harbor Merfolk

Gray Harbor Merfolk can't be blocked.
Gray Harbor Merfolk gets +2/+0 as long as you control a commander that's a creature or planeswalker.

Waterknot

Enchant creature
When Waterknot enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Jade Guardian

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
When Jade Guardian enters the battlefield, put a +1/+1 counter on target Merfolk you control.

Drake

Shipwreck Moray

When Shipwreck Moray enters the battlefield, you get {E}{E}{E}{E} (four energy counters).
Pay {E}: Shipwreck Moray gets +2/-2 until end of turn.

Dreadwaters

Target player mills X cards, where X is the number of lands you control.

River Darter

River Darter can't be blocked by Dinosaurs.

Capsizing Wave

Return target creature to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Sword Coast Serpent

Sword Coast Serpent can't be blocked as long as you've cast a noncreature spell this turn.

Sword Coast Serpent // Capsizing Wave

Wind Strider

Salvage Scuttler

Whenever Salvage Scuttler attacks, return an artifact you control to its owner's hand.

Crashing Tide

This spell has flash as long as you control a Merfolk.
Return target creature to its owner's hand.
Draw a card.

Run Aground

Put target artifact or creature on top of its owner's library.

Tishana's Wayfinder

When Tishana's Wayfinder enters the battlefield, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Negate

Leadership Vacuum

Target player returns each commander they control from the battlefield to the command zone.
Draw a card.

Sea God's Revenge

Return up to three target creatures your opponents control to their owners' hands. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Pull from the Deep

Return up to one target instant card and up to one target sorcery card from your graveyard to your hand. Exile Pull from the Deep.

Depths of Desire

Return target creature to its owner's hand. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Grip of the Roil

Surge {1}{U} (You may cast this spell for its surge cost if you or a teammate has cast another spell this turn.)
Tap target creature. It doesn't untap during its controller's next untap step.
Draw a card.

Treasure

{T}, Sacrifice this artifact: Add one mana of any color.

Incongruity

Exile target creature. That creature's controller creates a 3/3 green Frog Lizard creature token.

Incubation

Look at the top five cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Incubation // Incongruity

Mirrorshell Crab

Ward {3} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
Channel — {2}{U}, Discard Mirrorshell Crab: Counter target spell or ability unless its controller pays {3}.

Thassa's Emissary

Bestow {5}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Whenever Thassa's Emissary or enchanted creature deals combat damage to a player, draw a card.
Enchanted creature gets +3/+3.

Dreadlight Monstrosity

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
{3}{U}{U}: Dreadlight Monstrosity can't be blocked this turn. Activate only if you own a card in exile.

Sweep Away

Return target creature to its owner's hand. If that creature is attacking, you may put it on top of its owner's library instead.

Volshe Tideturner

{T}: Add {U}. Spend this mana only to cast an instant or sorcery spell or a kicked spell.

River Heralds' Boon

Put a +1/+1 counter on target creature and a +1/+1 counter on up to one target Merfolk.

Meteorite

When Meteorite enters the battlefield, it deals 2 damage to any target.
{T}: Add one mana of any color.

Wavecrash Triton

Heroic — Whenever you cast a spell that targets Wavecrash Triton, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Stormtide Leviathan

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
All lands are Islands in addition to their other types.
Creatures without flying or islandwalk can't attack.

Waker of Waves

Creatures your opponents control get -1/-0.
{1}{U}, Discard Waker of Waves: Look at the top two cards of your library. Put one of them into your hand and the other into your graveyard.

Thassa's Bounty

Draw three cards. Target player mills three cards.

Voda Sea Scavenger

Domain — When Voda Sea Scavenger enters the battlefield, look at the top X cards of your library, where X is the number of basic land types among lands you control. You may put one of those cards on top of your library. Put the rest on the bottom of your library in a random order.

Talrand's Invocation

Create two 2/2 blue Drake creature tokens with flying.

Dragon's Claw

Whenever a player casts a red spell, you may gain 1 life.

Tidal Surge

Tap up to three target creatures without flying.

Mantle of Tides

Equipped creature gets +1/+2.
Whenever you draw your second card each turn, attach Mantle of Tides to target creature you control.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Augur of Bolas

When Augur of Bolas enters the battlefield, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Storm Sculptor

Storm Sculptor can't be blocked.
When Storm Sculptor enters the battlefield, return a creature you control to its owner's hand.

Emperor Mihail II

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.

Pouncing Shoreshark

Mutate {3}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flash
Whenever this creature mutates, you may return target creature an opponent controls to its owner's hand.

Cancel

Island

Winterthorn Blessing

Put a +1/+1 counter on up to one target creature you control. Tap up to one target creature you don't control, and that creature doesn't untap during its controller's next untap step.
Flashback {1}{G}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Disrupt

Counter target instant or sorcery spell unless its controller pays {1}.
Draw a card.

Sea Monster

Sea Monster can't attack unless defending player controls an Island.

Jungle Delver

{3}{G}: Put a +1/+1 counter on Jungle Delver.

Vision of the Unspeakable

Flying, trample
Vision of the Unspeakable gets +1/+1 for each card in your hand.

Behold the Unspeakable

(As this Saga enters and after your draw step, add a lore counter.)
I — Creatures you don't control get -2/-0 until your next turn.
II — If you have one or fewer cards in hand, draw four cards. Otherwise, scry 2, then draw two cards.
III — Exile this Saga, then return it to the battlefield transformed under your control.

Behold the Unspeakable // Vision of the Unspeakable

Founding the Third Path

Read ahead (Choose a chapter and start with that many lore counters. Add one after your draw step. Skipped chapters don't trigger. Sacrifice after III.)
I — You may cast an instant or sorcery spell with mana value 1 or 2 from your hand without paying its mana cost.
II — Target player mills four cards.
III — Exile target instant or sorcery card from your graveyard. Copy it. You may cast the copy.

Towering-Wave Mystic

Whenever Towering-Wave Mystic deals damage, target player mills that many cards.

Aboshan's Desire

Enchant creature
Enchanted creature has flying.
Threshold — Enchanted creature has shroud as long as seven or more cards are in your graveyard. (It can't be the target of spells or abilities.)

Forest

Steelfin Whale

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Whenever an artifact enters the battlefield under your control, untap Steelfin Whale.

Thassa's Rebuff

Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Sealock Monster

Sealock Monster can't attack unless defending player controls an Island.
{5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Sealock Monster becomes monstrous, target land becomes an Island in addition to its other types.

Scroll Thief

Whenever Scroll Thief deals combat damage to a player, draw a card.

War-Wing Siren

Flying
Heroic — Whenever you cast a spell that targets War-Wing Siren, put a +1/+1 counter on War-Wing Siren.

Vortex Elemental

{U}: Put Vortex Elemental and each creature blocking or blocked by it on top of their owners' libraries, then those players shuffle.
{3}{U}{U}: Target creature blocks Vortex Elemental this turn if able.

Jungleborn Pioneer

When Jungleborn Pioneer enters the battlefield, create a 1/1 blue Merfolk creature token with hexproof. (It can't be the target of spells or abilities your opponents control.)