Have

Boomerang

Return target permanent to its owner's hand.

Tormod's Crypt

{T}, Sacrifice this artifact: Exile target player's graveyard.

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}.

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Hydroblast

Choose one —
• Counter target spell if it's red.
• Destroy target permanent if it's red.

Annul

Counter target artifact or enchantment spell.

Proxy

Misdirection

You may exile a blue card from your hand rather than pay this spell's mana cost.
Change the target of target spell with a single target.

Waterfront Bouncer

{U}, {T}, Discard a card: Return target creature to its owner's hand.

Seasinger

When you control no Islands, sacrifice this creature.
You may choose not to untap this creature during your untap step.
{T}: Gain control of target creature whose controller controls an Island for as long as you control this creature and this creature remains tapped.

Island

Reef Shaman

{T}: Target land becomes the basic land type of your choice until end of turn.

Opposition

Tap an untapped creature you control: Tap target artifact, creature, or land.

Saprazzan Heir

Whenever this creature becomes blocked, you may draw three cards.

Winter Orb

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

Whirlpool Warrior

When this creature enters, shuffle the cards from your hand into your library, then draw that many cards.
{R}, Sacrifice this creature: Each player shuffles the cards from their hand into their library, then draws that many cards.

Counterspell

Chill

Whirlpool Rider

When this creature enters, shuffle the cards from your hand into your library, then draw that many cards.

Rootwater Thief

{U}: This creature gains flying until end of turn.
Whenever this creature deals combat damage to a player, you may pay {2}. If you do, search that player's library for a card and exile it, then the player shuffles.

Back to Basics

Nonbasic lands don't untap during their controllers' untap steps.

Foil

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

Tidal Warrior

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

Curiosity

Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

Gush

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