Flow of Knowledge

Draw a card for each Island you control, then discard two cards.

Flooded Shoreline

{U}{U}, Return two Islands you control to their owner's hand: Return target creature to its owner's hand.

Merfolk Wayfinder

Flying
When Merfolk Wayfinder enters, reveal the top three cards of your library. Put all Island cards revealed this way into your hand and the rest on the bottom of your library in any order.

Spire Golem

Affinity for Islands (This spell costs {1} less to cast for each Island you control.)
Flying

Guardian of Tazeem

Flying
Landfall — Whenever a land you control enters, tap target creature an opponent controls. If that land is an Island, that creature doesn't untap during its controller's next untap step.

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.

Tidewalker

Tidewalker enters with a time counter on it for each Island you control.
Vanishing (At the beginning of your upkeep, remove a time counter from this creature. When the last is removed, sacrifice it.)
Tidewalker's power and toughness are each equal to the number of time counters on it.

Scourge of Fleets

When Scourge of Fleets 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.

Vedalken Shackles

You may choose not to untap Vedalken Shackles during your untap step.
{2}, {T}: Gain control of target creature with power less than or equal to the number of Islands you control for as long as Vedalken Shackles remains tapped.

Mu Yanling, Sky Dancer

+2: Until your next turn, up to one target creature gets -2/-0 and loses flying.
−3: Create a 4/4 blue Elemental Bird creature token with flying.
−8: You get an emblem with "Islands you control have '{T}: Draw a card.'"

Coastal Bulwark

Defender
Coastal Bulwark gets +2/+0 as long as you control an Island.
{2}, {T}: Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

Walk the Aeons

Buyback—Sacrifice three Islands. (You may sacrifice three Islands in addition to any other costs as you cast this spell. If you do, put this card into your hand as it resolves.)
Target player takes an extra turn after this one.

Foil

You may discard an Island card and another card rather than pay this spell's mana cost.
Counter target spell.

Spectral Deluge

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.
Foretell {1}{U}{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.)

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.

Ensnare

You may return two Islands you control to their owner's hand rather than pay this spell's mana cost.
Tap all creatures.

Staff of the Mind Magus

Whenever you cast a blue spell or an Island you control enters, you gain 1 life.

Wonder

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

Tidal Bore

You may return an Island you control to its owner's hand rather than pay this spell's mana cost.
You may tap or untap target creature.

Psychic Allergy

As Psychic Allergy enters, choose a color.
At the beginning of each opponent's upkeep, Psychic Allergy deals X damage to that player, where X is the number of nontoken permanents of the chosen color they control.
At the beginning of your upkeep, destroy Psychic Allergy unless you sacrifice two Islands.

Flow of Ideas

Engulf the Shore

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

Gush

You may return two Islands you control to their owner's hand rather than pay this spell's mana cost.
Draw two cards.

Tempest Djinn

Flying
This creature gets +1/+0 for each basic Island you control.

Submerge

If an opponent controls a Forest and you control an Island, you may cast this spell without paying its mana cost.
Put target creature on top of its owner's library.

Floodgate

Defender
When Floodgate has flying, sacrifice it.
When Floodgate leaves the battlefield, it deals damage to each nonblue creature without flying equal to half the number of Islands you control, rounded down.

Saprazzan Legate

If an opponent controls a Mountain and you control an Island, you may cast this spell without paying its mana cost.
Flying

Thwart

You may return three Islands you control to their owner's hand rather than pay this spell's mana cost.
Counter target spell.

Kraken of the Straits

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

Armored Galleon

Armored Galleon can't attack unless defending player controls an Island.

Charix, the Raging Isle

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

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}.

Genju of the Falls

Enchant Island
{2}: Enchanted Island becomes a 3/2 blue Spirit creature with flying until end of turn. It's still a land.
When enchanted Island is put into a graveyard, you may return Genju of the Falls from your graveyard to your hand.