Tidal Warrior

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

Wonder

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

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

Whenever Saprazzan Heir becomes blocked, you may draw three cards.

Target player draws two cards.
Flashback—{1}{U}, Pay 3 life. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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

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

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}.

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

When Vodalian Merchant enters, draw a card, then discard a card.

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