Dirgur Nemesis

Defender
Megamorph {6}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)

Vodalian Serpent

Kicker {2} (You may pay an additional {2} as you cast this spell.)
Vodalian Serpent can't attack unless defending player controls an Island.
If Vodalian Serpent was kicked, it enters with four +1/+1 counters on it.

Island

Frilled Sea Serpent

{5}{U}{U}: Frilled Sea Serpent can't be blocked this turn.

Cephalid Aristocrat

Whenever Cephalid Aristocrat becomes the target of a spell or ability, mill two cards.

Armillary Sphere

{2}, {T}, Sacrifice Armillary Sphere: Search your library for up to two basic land cards, reveal them, put them into your hand, then shuffle.

Cryptic Serpent

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.

Deep-Sea Terror

Deep-Sea Terror can't attack unless there are seven or more cards in your graveyard.

Godhunter Octopus

Godhunter Octopus can't attack unless defending player controls an enchantment or an enchanted permanent.

Slipstream Serpent

Slipstream Serpent can't attack unless defending player controls an Island.
When you control no Islands, sacrifice Slipstream Serpent.
Morph {5}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Floodtide Serpent

Floodtide Serpent can't attack unless you return an enchantment you control to its owner's hand. (This cost is paid as attackers are declared.)

Dreamwinder

Dreamwinder can't attack unless defending player controls an Island.
{U}, Sacrifice an Island: Target land becomes an Island until end of turn.

Kukemssa Serpent

Kukemssa Serpent can't attack unless defending player controls an Island.
{U}, Sacrifice an Island: Target land an opponent controls becomes an Island until end of turn.
When you control no Islands, sacrifice Kukemssa Serpent.

Shoal Serpent

Defender
Landfall — Whenever a land you control enters, Shoal Serpent loses defender until end of turn.

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

Cephalid Looter

{T}: Target player draws a card, then discards a card.

Tidal Terror

Whenever Tidal Terror attacks, you may tap two other untapped creatures you control. If you do, Tidal Terror 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.)

Kiora's Dambreaker

When Kiora's Dambreaker enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Cephalid Sage

Threshold — As long as seven or more cards are in your graveyard, Cephalid Sage has "When Cephalid Sage enters, draw three cards, then discard two cards."

Gearseeker Serpent

This spell costs {1} less to cast for each artifact you control.
{5}{U}: Gearseeker Serpent can't be blocked this turn.

Ancestral Reminiscence

Kraken Hatchling

Spire Serpent

Defender
Metalcraft — As long as you control three or more artifacts, Spire Serpent gets +2/+2 and can attack as though it didn't have defender.

Bubble Smuggler

Disguise {5}{U} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
As Bubble Smuggler is turned face up, put four +1/+1 counters on it.

Tidal Warrior

{T}: Target land becomes an Island until end of turn.

Scrapdiver Serpent

Scrapdiver Serpent can't be blocked as long as defending player controls an artifact.

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.)

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.)

Serpent of the Endless Sea

Serpent of the Endless Sea's power and toughness are each equal to the number of Islands you control.
Serpent of the Endless Sea can't attack unless defending player controls an Island.

Giant Octopus

Adventuring Gear

Landfall — Whenever a land you control enters, equipped creature gets +2/+2 until end of turn.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Tolarian Terror

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)

Backstreet Bruiser

Defender
As long as there are two or more counters among creatures you control, Backstreet Bruiser can attack as though it didn't have defender.

Harbor Serpent

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Harbor Serpent can't attack unless there are five or more Islands on the battlefield.

Aquitect's Will

Put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. If you control a Merfolk, draw a card.

Sea Serpent

Sea Serpent can't attack unless defending player controls an Island.
When you control no Islands, sacrifice Sea Serpent.

Octoprophet

When Octoprophet 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.)

Slinn Voda, the Rising Deep

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