Dismal Backwater

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {B}.

Slinn Voda, the Rising Deep

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
When Slinn Voda enters, if it was kicked, return all creatures to their owners' hands except for Merfolk, Krakens, Leviathans, Octopuses, and Serpents.

Gravewaker

Flying (This creature can't be blocked except by creatures with flying or reach.)
{5}{B}{B}: Return target creature card from your graveyard to the battlefield tapped.

River Sneak

This creature can't be blocked.
Whenever another Merfolk you control enters, this creature gets +1/+1 until end of turn.

Icebreaker Kraken

Affinity for snow lands (This spell costs {1} less to cast for each snow land you control.)
When this creature enters, artifacts and creatures target opponent controls don't untap during that player's next untap step.
Return three snow lands you control to their owner's hand: Return this creature to its owner's hand.

Submerged Boneyard

This land enters tapped.
{T}: Add {U} or {B}.

Hostile Negotiations

Exile the top three cards of your library in a face-down pile, then exile the top three cards of your library in another face-down pile. Look at the cards in each pile, then turn a pile of your choice face up. An opponent chooses one of those piles. Put that pile into your hand and the other into your graveyard. You lose 3 life.

Startling Development

Until end of turn, target creature becomes a blue Serpent with base power and toughness 4/4.
Cycling {1} ({1}, Discard this card: Draw a card.)

Wonder

Flying
As long as this card is in your graveyard and you control an Island, creatures you control have flying.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Spined Megalodon

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

In Bolas's Clutches

Enchant permanent
You control enchanted permanent.
Enchanted permanent is legendary.

Deep-Sea Kraken

This creature can't be blocked.
Suspend 9—{2}{U} (Rather than cast this card from your hand, you may pay {2}{U} and exile it with nine time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)
Whenever an opponent casts a spell, if this card is suspended, remove a time counter from it.

Tomebound Lich

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Whenever this creature enters or deals combat damage to a player, draw a card, then discard a card.

Entrancing Lyre

You may choose not to untap this artifact during your untap step.
{X}, {T}: Tap target creature with power X or less. It doesn't untap during its controller's untap step for as long as this artifact remains tapped.

Serpent of Yawning Depths

Krakens, Leviathans, Octopuses, and Serpents you control can't be blocked except by Krakens, Leviathans, Octopuses, and Serpents.

The Trickster-God's Heist

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — You may exchange control of two target creatures.
II — You may exchange control of two target nonbasic, noncreature permanents that share a card type.
III — Target player loses 3 life and you gain 3 life.

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.

Filter Out

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

Snow-Covered Island

Frilled Sea Serpent

{5}{U}{U}: This creature can't be blocked this turn.

Rona, Tolarian Obliterator

Trample
Whenever a source deals damage to Rona, that source's controller exiles a card from their hand at random. If it's a land card, you may put it onto the battlefield under your control. Otherwise, you may cast it without paying its mana cost.

Rona, Herald of Invasion

Whenever you cast a legendary spell, untap Rona.
{T}: Draw a card, then discard a card.
{5}{B/P}: Transform Rona. Activate only as a sorcery. ({B/P} can be paid with either {B} or 2 life.)

Rona, Herald of Invasion // Rona, Tolarian Obliterator

Cavern Whisperer

Mutate {3}{B} (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.)
Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature mutates, each opponent discards a card.

Nezahal, Primal Tide

This spell can't be countered.
You have no maximum hand size.
Whenever an opponent casts a noncreature spell, draw a card.
Discard three cards: Exile Nezahal. Return it to the battlefield tapped under its owner's control at the beginning of the next end step.

Thassa, God of the Sea

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
At the beginning of your upkeep, scry 1.
{1}{U}: Target creature you control can't be blocked this turn.

Swamp

Rakshasa Debaser

Whenever this creature attacks, put target creature card from defending player's graveyard onto the battlefield under your control.
Encore {6}{B}{B} ({6}{B}{B}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Archipelagore

Mutate {5}{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.)
Whenever this creature mutates, tap up to X target creatures, where X is the number of times this creature has mutated. Those creatures don't untap during their controller's next untap step.

Gyruda, Doom of Depths

Companion — Your starting deck contains only cards with even mana values. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
When Gyruda enters, each player mills four cards. Put a creature card with an even mana value from among the milled cards onto the battlefield under your control.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

King Narfi's Betrayal

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Each player mills four cards. Then you may exile a creature or planeswalker card from each graveyard.
II, III — Until end of turn, you may cast spells from among cards exiled with this Saga, and you may spend mana as though it were mana of any color to cast those spells.

Island

Merfolk Trickster

Flash
When this creature enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Unknown Shores

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

Snow-Covered Swamp

Shimmering Grotto

Dreamtail Heron

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.)
Flying
Whenever this creature mutates, draw a card.

Reconnaissance Mission

Whenever a creature you control deals combat damage to a player, you may draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

Overloaded Mage-Ring

{1}, {T}, Sacrifice this artifact: Copy target spell you control. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.)

Invasion of Vryn

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When this Siege enters, draw three cards, then discard a card.

Invasion of Vryn // Overloaded Mage-Ring

Show and Tell

Each player may put an artifact, creature, enchantment, or land card from their hand onto the battlefield.

Riddlemaster Sphinx

Flying (This creature can't be blocked except by creatures with flying or reach.)
When this creature enters, you may return target creature an opponent controls to its owner's hand.

Pollywog Symbiote

Each creature spell you cast costs {1} less to cast if it has mutate.
Whenever you cast a creature spell, if it has mutate, draw a card, then discard a card.

Mystic Redaction

At the beginning of your upkeep, scry 1.
Whenever you discard a card, each opponent mills two cards. (They put the top two cards of their library into their graveyard.)

Mnemonic Betrayal

Exile all opponents' graveyards. You may cast spells from among those cards this turn, and mana of any type can be spent to cast them. At the beginning of the next end step, if any of those cards remain exiled, return them to their owners' graveyards.
Exile Mnemonic Betrayal.

Sol Ring

Insatiable Hemophage

Mutate {2}{B} (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.)
Deathtouch
Whenever this creature mutates, each opponent loses X life and you gain X life, where X is the number of times this creature has mutated.

Saw It Coming

Counter target spell.
Foretell {1}{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.)

Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Covetous Urge

Target opponent reveals their hand. You choose a nonland card from that player's graveyard or hand and exile it. You may cast that 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.

Marvo, Deep Operative

Whenever Marvo attacks, clash with defending player. (Each clashing player reveals the top card of their library, then puts that card on their choice of the top or bottom. A player wins if their card had a greater mana value.)
Whenever you win a clash, draw a card. Then you may cast a spell from your hand with mana value 8 or less without paying its mana cost.

Elder Deep-Fiend

Flash
Emerge {5}{U}{U} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
When you cast this spell, tap up to four target permanents.

Callaphe, Beloved of the Sea

Callaphe's power is equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
Creatures and enchantments you control have "Spells your opponents cast that target this permanent cost {1} more to cast."

Voracious Greatshark

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, counter target artifact or creature spell.

Entrancing Melody

Gain control of target creature with mana value X.

Psychic Symbiont

Flying
When this creature enters, target opponent discards a card and you draw a card.

Krothuss, Lord of the Deep

Flying
Whenever Krothuss attacks, create a tapped and attacking token that's a copy of another target attacking creature. If that creature is a Kraken, Leviathan, Octopus, or Serpent, create two of those tokens instead.

Runo Stromkirk

Flying
When Runo enters, put up to one target creature card from your graveyard on top of your library.
At the beginning of your upkeep, look at the top card of your library. You may reveal that card. If a creature card with mana value 6 or greater is revealed this way, transform Runo.

Runo Stromkirk // Krothuss, Lord of the Deep

Phase Dolphin

Whenever this creature attacks, another target attacking creature can't be blocked this turn.

Screaming Swarm

Flying
Whenever you attack with one or more creatures, target player mills that many cards. (To mill a card, a player puts the top card of their library into their graveyard.)
{2}{U}: Put this card from your graveyard into your library second from the top.

Dimir Guildgate

Blitz Leech

Flash
When this creature enters, target creature an opponent controls gets -2/-2 until end of turn. Remove all counters from that creature.

Brainstorm

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

Glen Elendra Liege

Flying
Other blue creatures you control get +1/+1.
Other black creatures you control get +1/+1.

Brinelin, the Moon Kraken

When Brinelin enters and whenever you cast a spell with mana value 6 or greater, you may return target nonland permanent to its owner's hand.
Partner (You can have two commanders if both have partner.)

Hive of the Eye Tyrant

If you control two or more other lands, this land enters tapped.
{T}: Add {B}.
{3}{B}: Until end of turn, this land becomes a 3/3 black Beholder creature with menace and "Whenever this creature attacks, exile target card from defending player's graveyard." It's still a land.

Port of Karfell

This land enters tapped.
{T}: Add {U}.
{3}{U}{B}{B}, {T}, Sacrifice this land: Mill four cards, then return a creature card from your graveyard to the battlefield tapped. (To mill a card, put the top card of your library into your graveyard.)

Mirror Box

The "legend rule" doesn't apply to permanents you control.
Each legendary creature you control gets +1/+1.
Each nontoken creature you control gets +1/+1 for each other creature you control with the same name as that creature.

Spawning Kraken

Whenever a Kraken, Leviathan, Octopus, or Serpent you control deals combat damage to a player, create a 9/9 blue Kraken creature token.

Hullbreaker Horror

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.

Counterspell

Feywild Visitor

Commander creatures you own have "Whenever one or more nontoken creatures you control deal combat damage to a player, you create a 1/1 blue Faerie Dragon creature token with flying."

Extraplanar Lens

Imprint — When this artifact enters, you may exile target land you control.
Whenever a land with the same name as the exiled card is tapped for mana, its controller adds one mana of any type that land produced.

Aven Fateshaper

Flying
When this creature enters, look at the top four cards of your library, then put them back in any order.
{4}{U}: Look at the top four cards of your library, then put them back in any order.

Lorthos, the Tidemaker

Whenever Lorthos attacks, you may pay {8}. If you do, tap up to eight target permanents. Those permanents don't untap during their controllers' next untap steps.

Horizon Scholar

Flying
When this creature enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Chittering Harvester

Mutate {4}{B} (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.)
Whenever this creature mutates, each opponent sacrifices a creature of their choice.

Trench Behemoth

Return a land you control to its owner's hand: Untap this creature. It gains hexproof until end of turn.
Landfall — Whenever a land you control enters, target creature an opponent controls attacks during its controller's next combat phase if able.