Island

Vineshaper Mystic

When this creature enters, put a +1/+1 counter on each of up to two target Merfolk you control.

Merfolk Skydiver

Flying
When this creature enters, put a +1/+1 counter on target creature you control.
{3}{G}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Deeproot Waters

Whenever you cast a Merfolk spell, create a 1/1 blue Merfolk creature token with hexproof. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

Crashing Tide

This spell has flash as long as you control a Merfolk.
Return target creature to its owner's hand.
Draw a card.

Watertrap Weaver

When this creature enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Jade Bearer

When this creature enters, put a +1/+1 counter on another target Merfolk you control.

Storm Sculptor

This creature can't be blocked.
When this creature enters, return a creature you control to its owner's hand.

Zameck Guildmage

{G}{U}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{G}{U}, Remove a +1/+1 counter from a creature you control: Draw a card.

Jungle Delver

{3}{G}: Put a +1/+1 counter on this creature.

Combine Guildmage

{1}{G}, {T}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{1}{U}, {T}: Move a +1/+1 counter from target creature you control onto another target creature you control.

Shaper Apprentice

This creature has flying as long as you control another Merfolk.

Forest

River Heralds' Boon

Put a +1/+1 counter on target creature and a +1/+1 counter on up to one target Merfolk.

Jade Guardian

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
When this creature enters, put a +1/+1 counter on target Merfolk you control.

Courage in Crisis

Put a +1/+1 counter on target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Kumena's Speaker

This creature gets +1/+1 as long as you control another Merfolk or an Island.

Merfolk Mistbinder

Vorel of the Hull Clade

{G}{U}, {T}: Double the number of each kind of counter on target artifact, creature, or land.

Mist-Cloaked Herald

Woodland Stream

This land enters tapped.
{T}: Add {G} or {U}.

Tempest Caller

When this creature enters, tap all creatures target opponent controls.

Jungleborn Pioneer

When this creature enters, create a 1/1 blue Merfolk creature token with hexproof. (It can't be the target of spells or abilities your opponents control.)

Shapers of Nature

{3}{G}: Put a +1/+1 counter on target creature.
{2}{U}, Remove a +1/+1 counter from a creature you control: Draw a card.

Cold-Eyed Selkie

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever this creature deals combat damage to a player, you may draw that many cards.

New Horizons

Enchant land
When this Aura enters, put a +1/+1 counter on target creature you control.
Enchanted land has "{T}: Add two mana of any one color."