Merrow Harbinger

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
When this creature enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.

Plains

Judge of Currents

Whenever a Merfolk you control becomes tapped, you may gain 1 life.

Rings of Brighthearth

Whenever you activate an ability, if it isn't a mana ability, you may pay {2}. If you do, copy that ability. You may choose new targets for the copy.

Island

Merrow Reejerey

Other Merfolk creatures you control get +1/+1.
Whenever you cast a Merfolk spell, you may tap or untap target permanent.

Wanderwine Prophets

Champion a Merfolk (When this enters, sacrifice it unless you exile another Merfolk you control. When this leaves the battlefield, that card returns to the battlefield.)
Whenever this creature deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.

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.

Puresight Merrow

{W/U}, {Q}: Look at the top card of your library. You may exile that card. ({Q} is the untap symbol.)

Sygg, River Guide

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
{1}{W}: Target Merfolk you control gains protection from the color of your choice until end of turn.

Streambed Aquitects

{T}: Target Merfolk creature gets +1/+1 and gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)
{T}: Target land becomes an Island until end of turn.

Banishing Knack

Until end of turn, target creature gains "{T}: Return target nonland permanent to its owner's hand."

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Wake Thrasher

Whenever a permanent you control becomes untapped, this creature gets +1/+1 until end of turn.

Veteran of the Depths

Whenever this creature becomes tapped, you may put a +1/+1 counter on it.

Lord of Atlantis

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

Stonybrook Schoolmaster

Whenever this creature becomes tapped, you may create a 1/1 blue Merfolk Wizard creature token.

Merrow Commerce

At the beginning of your end step, untap all Merfolk you control.

Galina's Knight

Summon the School

Create two 1/1 blue Merfolk Wizard creature tokens.
Tap four untapped Merfolk you control: Return this card from your graveyard to your hand.

Harpoon Sniper

{W}, {T}: This creature deals X damage to target attacking or blocking creature, where X is the number of Merfolk you control.

Leech Bonder

This creature enters with two -1/-1 counters on it.
{U}, {Q}: Move a counter from target creature onto a second target creature. ({Q} is the untap symbol.)