Island

Manta Ray

Manta Ray can't attack unless defending player controls an Island.
Manta Ray can't be blocked except by blue creatures.
When you control no Islands, sacrifice Manta Ray.

Phantom Wings

Enchant creature
Enchanted creature has flying.
Sacrifice Phantom Wings: Return enchanted creature to its owner's hand.

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

Spreading Seas

Enchant land
When Spreading Seas enters, draw a card.
Enchanted land is an Island.

Sea's Claim

Enchant land (Target a land as you cast this. This card enters attached to that land.)
Enchanted land is an Island.

Ponder

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

Apprentice Wizard

Sleight of Hand

Look at the top two cards of your library. Put one of them into your hand and the other on the bottom of your library.

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.

Dandân

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

Mana Leak

Counter target spell unless its controller pays {3}.

Contact Other Plane

Roll a d20.
1—9 | Draw two cards.
10—19 | Scry 2, then draw two cards.
20 | Scry 3, then draw three cards.

Hammerhead Shark

Hammerhead Shark can't attack unless defending player controls an Island.

Preordain

Scry 2, then draw a card. (To 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.)

Grayscaled Gharial

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