Manta Riders

{U}: Manta Riders gains flying until end of turn.

Accumulated Knowledge

Draw a card, then draw cards equal to the number of cards named Accumulated Knowledge in all graveyards.

Counterspell

Island

Hibernation

Return all green permanents to their owners' hands.

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.

Lonely Sandbar

Lonely Sandbar enters tapped.
{T}: Add {U}.
Cycling {U} ({U}, Discard this card: Draw a card.)

Annul

Counter target artifact or enchantment spell.

Tidal Warrior

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

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Merfolk Traders

When Merfolk Traders enters, draw a card, then discard a card.

Wasteland

{T}: Add {C}.
{T}, Sacrifice Wasteland: Destroy target nonbasic land.

Rootwater Hunter

{T}: Rootwater Hunter deals 1 damage to any target.

Force of Will

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost.
Counter target spell.

Gush

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

Waterfront Bouncer

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

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.

Blue Elemental Blast

Choose one —
• Counter target red spell.
• Destroy target red permanent.

Lord of Atlantis

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