Caetus, Sea Tyrant of Segovia

Noncreature spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a noncreature spell pays for {1} or one mana of that creature's color.)
At the beginning of your end step, untap up to four target creatures.

Invasion of Segovia

(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, create two 1/1 blue Kraken creature tokens with trample.

Invasion of Segovia // Caetus, Sea Tyrant of Segovia

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Bojuka Bog

This land enters tapped.
When this land enters, exile target player's graveyard.
{T}: Add {B}.

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Bident of Thassa

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.

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.

Tidal Terror

Whenever this creature attacks, you may tap two other untapped creatures you control. If you do, this creature can't be blocked this turn.
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

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.

Lochmere Serpent

Flash
{U}, Sacrifice an Island: This creature can't be blocked this turn.
{B}, Sacrifice a Swamp: You gain 1 life and draw a card.
{U}{B}: Exile five target cards from an opponent's graveyard. Return this card from your graveyard to your hand. Activate only as a sorcery.

Junk Winder

Affinity for tokens (This spell costs {1} less to cast for each token you control.)
Whenever a token you control enters, tap target nonland permanent an opponent controls. It doesn't untap during its controller's next untap step.

Drowned Catacomb

This land enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Scourge of Fleets

When this creature enters, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.

Temple of the False God

{T}: Add {C}{C}. Activate only if you control five or more lands.

Darkslick Shores

This land enters tapped unless you control two or fewer other lands.
{T}: Add {U} or {B}.

Nephalia Academy

If a spell or ability an opponent controls causes you to discard a card, you may reveal that card and put it on top of your library instead of putting it anywhere else.
{T}: Add {C}.

Undercity Sewers

({T}: Add {U} or {B}.)
This land enters tapped.
When this land enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

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.)

Sea-Dasher Octopus

Mutate {1}{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 deals combat damage to a player, draw a card.

Darkwater Catacombs

Charix, the Raging Isle

Spells your opponents cast that target Charix cost {2} more to cast.
{3}: Charix gets +X/-X until end of turn, where X is the number of Islands you control.

Sol Ring

Tainted Isle

{T}: Add {C}.
{T}: Add {U} or {B}. Activate only if you control a Swamp.

Evolving Wilds

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

Sigiled Starfish

{T}: Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Stormsurge Kraken

Hexproof
Lieutenant — As long as you control your commander, this creature gets +2/+2 and has "Whenever this creature becomes blocked, you may draw two cards."

The Reality Chip

You may look at the top card of your library any time.
As long as The Reality Chip is attached to a creature, you may play lands and cast spells from the top of your library.
Reconfigure {2}{U} ({2}{U}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Swamp

Serpent of Yawning Depths

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

Nemesis of Reason

Whenever this creature attacks, defending player mills ten cards.

Morphic Pool

This land enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Llawan, Cephalid Empress

When Llawan enters, return all blue creatures your opponents control to their owners' hands.
Your opponents can't cast blue creature spells.

Dimir Signet

Thran Dynamo

Hedron Archive

{T}: Add {C}{C}.
{2}, {T}, Sacrifice this artifact: Draw two cards.

Night's Whisper

Path of Ancestry

This land enters 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.)

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. This artifact deals 1 damage to you.

Sinister Starfish

{T}: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Sunken Ruins

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

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.

River Serpent

This creature can't attack unless there are five or more cards in your graveyard.
Cycling {U} ({U}, Discard this card: Draw a card.)

Inkwell Leviathan

Trample
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Shroud (This creature can't be the target of spells or abilities.)

Kozilek's Unsealing

Devoid (This card has no color.)
Whenever you cast a creature spell with mana value 4, 5, or 6, create two 0/1 colorless Eldrazi Spawn creature tokens with "Sacrifice this token: Add {C}."
Whenever you cast a creature spell with mana value 7 or greater, draw three cards.

Counterspell

Fetid Pools

({T}: Add {U} or {B}.)
This land enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Gloomlake Verge

{T}: Add {U}.
{T}: Add {B}. Activate only if you control an Island or a Swamp.

Choked Estuary

As this land enters, you may reveal an Island or Swamp card from your hand. If you don't, this land enters tapped.
{T}: Add {U} or {B}.

Summon: Leviathan

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Return each creature that isn't a Kraken, Leviathan, Merfolk, Octopus, or Serpent to its owner's hand.
II, III — Until end of turn, whenever a Kraken, Leviathan, Merfolk, Octopus, or Serpent attacks, draw a card.
Ward {2}

Dimir Aqueduct

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {U}{B}.

Benthic Behemoth

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Island

Polluted Delta

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

Trench Gorger

Trample
When this creature enters, you may search your library for any number of land cards, exile them, then shuffle. If you do, this creature has base power and base toughness each equal to the number of cards exiled this way.

Inevitable Betrayal

Suspend 3—{1}{U}{U} (Rather than cast this card from your hand, pay {1}{U}{U} and exile it with three 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.)
Search target opponent's library for a creature card and put that card onto the battlefield under your control. Then that player shuffles.

Dismember

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

Temple of Deceit

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {U} or {B}.

Quicksilver Amulet

{4}, {T}: You may put a creature card from your hand onto the battlefield.

Grappling Kraken

Landfall — Whenever a land you control enters, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Kraken of the Straits

Creatures with power less than the number of Islands you control can't block this creature.

Commander's Sphere

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

Toxrill, the Corrosive

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.

Shipwreck Marsh

This land enters tapped unless you control two or more other lands.
{T}: Add {U} or {B}.

Brainstorm

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

Shipbreaker Kraken

{6}{U}{U}: Monstrosity 4. (If this creature isn't monstrous, put four +1/+1 counters on it and it becomes monstrous.)
When this creature becomes monstrous, tap up to four target creatures. Those creatures don't untap during their controllers' untap steps for as long as you control this creature.

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.

Underground River

{T}: Add {C}.
{T}: Add {U} or {B}. This land deals 1 damage to you.

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.

Command Tower

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

Watery Grave

({T}: Add {U} or {B}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Quest for Ula's Temple

At the beginning of your upkeep, you may look at the top card of your library. If it's a creature card, you may reveal it and put a quest counter on this enchantment.
At the beginning of each end step, if there are three or more quest counters on this enchantment, you may put a Kraken, Leviathan, Octopus, or Serpent creature card from your hand onto the battlefield.

Gilded Lotus

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

The Grim Captain's Locker

{T}: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
{T}: Until end of turn, each creature card in your graveyard gains "Escape—{3}{B}, Exile four other cards from your graveyard." (You may cast a card with escape from your graveyard for its escape cost.)

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Halimar Depths

This land enters tapped.
When this land enters, look at the top three cards of your library, then put them back in any order.
{T}: Add {U}.

Reservoir Kraken

Trample, ward {2}
At the beginning of each combat, if this creature is untapped, any opponent may tap an untapped creature they control. If they do, tap this creature and create a 1/1 blue Fish creature token with "This token can't be blocked."

Cephalid Facetaker

This creature can't be blocked.
At the beginning of combat on your turn, you may have this creature become a copy of another target creature until end of turn, except it's 1/4 and has "This creature can't be blocked."

Force of Despair

If it's not your turn, you may exile a black card from your hand rather than pay this spell's mana cost.
Destroy all creatures that entered this turn.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Nadir Kraken

Whenever you draw a card, you may pay {1}. If you do, put a +1/+1 counter on this creature and create a 1/1 blue Tentacle creature token.

Gearseeker Serpent

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
{5}{U}: This creature can't be blocked this turn.

Myriad Landscape

This land enters tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice this land: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.

Sunken Hollow

({T}: Add {U} or {B}.)
This land enters tapped unless you control two or more basic lands.

Daggermaw Megalodon

Vigilance
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Striped Riverwinder

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Cycling {U} ({U}, Discard this card: Draw a card.)

Aboleth Spawn

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

River of Tears

{T}: Add {U}. If you played a land this turn, add {B} instead.

Starwinder

Whenever a creature you control deals combat damage to a player, you may draw that many cards.
Warp {2}{U}{U} (You may cast this card from your hand for its warp cost. Exile this creature at the beginning of the next end step, then you may cast it from exile on a later turn.)

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Grazilaxx, Illithid Scholar

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.

Arcane Signet

Daze

You may return an Island you control to its owner's hand rather than pay this spell's mana cost.
Counter target spell unless its controller pays {1}.