Vineshaper Mystic

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

Deeproot Warrior

Whenever this creature becomes blocked, it gets +1/+1 until end of turn.

Ixalli's Diviner

When this creature enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Deeproot Champion

Whenever you cast a noncreature spell, put a +1/+1 counter on this creature.

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.

Kumena's Speaker

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

Siren Lookout

Flying
When this creature enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Tishana's Wayfinder

Wind Strider

Flash (You may cast this spell any time you could cast an instant.)
Flying

Headwater Sentries

Shore Keeper

{7}{U}, {T}, Sacrifice this creature: Draw three cards.

Tishana, Voice of Thunder

Tishana's power and toughness are each equal to the number of cards in your hand.
You have no maximum hand size.
When Tishana enters, draw a card for each creature you control.

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.

Merfolk Branchwalker

Wildgrowth Walker

Whenever a creature you control explores, put a +1/+1 counter on this creature and you gain 3 life.