Water Elemental

Sea Serpent

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

Merchant Ship

Merchant Ship can't attack unless defending player controls an Island.
Whenever Merchant Ship attacks and isn't blocked, you gain 2 life.
When you control no Islands, sacrifice Merchant Ship.

Deep-Sea Serpent

Deep-Sea Serpent can't attack unless defending player controls an Island.

Bouncing Beebles

Bouncing Beebles can't be blocked as long as defending player controls an artifact.

Wall of Kelp

Defender (This creature can't attack.)
{U}{U}, {T}: Create a 0/1 blue Plant Wall creature token with defender named Kelp.

Rishadan Airship

Flying
Rishadan Airship can block only creatures with flying.

Teferi's Drake

Flying
Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)

Symbol of Unsummoning

Return target creature to its owner's hand.
Draw a card.

Blind Seer

{1}{U}: Target spell or permanent becomes the color of your choice until end of turn.

Unsummon

Return target creature to its owner's hand.

Control Magic

Enchant creature
You control enchanted creature.

Command of Unsummoning

Cast this spell only during the declare attackers step and only if you've been attacked this step.
Return one or two target attacking creatures to their owner's hand.

Ghost Ship

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.

Empress Galina

{U}{U}, {T}: Gain control of target legendary permanent. (This effect lasts indefinitely.)

Wu Warship

Wu Warship can't attack unless defending player controls an Island.

Talas Air Ship

Shipwreck Looter

Raid — When Shipwreck Looter enters, if you attacked this turn, you may draw a card. If you do, discard a card.

Shipwreck Dowser

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When this creature enters, return target instant or sorcery card from your graveyard to your hand.

Brine Hag

When Brine Hag dies, change the base power and toughness of all creatures that dealt damage to it this turn to 0/2. (This effect lasts indefinitely.)

Dandân

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

Howling Mine

At the beginning of each player's draw step, if Howling Mine is untapped, that player draws an additional card.

Winter Orb

As long as Winter Orb is untapped, players can't untap more than one land during their untap steps.

Shipwreck Moray

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

Merfolk of the Pearl Trident

Bubbling Beebles

Bubbling Beebles can't be blocked as long as defending player controls an enchantment.

Shipwreck Sentry

Defender
As long as an artifact entered the battlefield under your control this turn, Shipwreck Sentry can attack as though it didn't have defender.

Pirate Ship

Pirate Ship can't attack unless defending player controls an Island.
{T}: Pirate Ship deals 1 damage to any target.
When you control no Islands, sacrifice Pirate Ship.

Spiny Starfish

{U}: Regenerate Spiny Starfish.
At the beginning of each end step, if Spiny Starfish regenerated this turn, create a 0/1 blue Starfish creature token for each time it regenerated this turn.

Phantom Monster

The Omenkeel

Whenever a Vehicle you control deals combat damage to a player, that player exiles that many cards from the top of their library. You may play lands from among those cards for as long as they remain exiled.
Crew 1

Cosima, God of the Voyage

At the beginning of your upkeep, you may exile Cosima. If you do, it gains "Whenever a land you control enters, if Cosima is exiled, you may put a voyage counter on it. If you don't, return Cosima to the battlefield with X +1/+1 counters on it and draw X cards, where X is the number of voyage counters on it."