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

Islandwalk (This creature can't be blocked as long as defending player controls an Island.) {1}, {T}: Tap target land.

({T}: Add {U}.)

{T}: Add {C}. {1}: This land becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Flash When this creature enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Flash When this creature enters, counter up to one target activated or triggered ability. If an ability of an artifact, creature, or planeswalker is countered this way, that permanent loses all abilities for as long as this creature remains on the battlefield. (Mana abilities can't be targeted.)

Choose target spell or permanent that's red or green. Its owner puts it on their choice of the top or bottom of their library.

Activated abilities of creatures can't be activated.

You may cast this card as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.) When this creature enters, you may return target tapped creature an opponent controls to its owner's hand.

Counter target spell unless its controller pays {3}.

{T}: Target player exiles a card from their graveyard. {1}, Exile this artifact: Exile all graveyards. Draw a card.