Grasping Current

Return up to two target creatures to their owner's hand.
Search your library and/or graveyard for a card named Jace, Ingenious Mind-Mage, reveal it, and put it into your hand. If you searched your library this way, shuffle.

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.)

Kopala, Warden of Waves

Spells your opponents cast that target a Merfolk you control cost {2} more to cast.
Abilities your opponents activate that target a Merfolk you control cost {2} more to activate.

Woodland Stream

Woodland Stream enters tapped.
{T}: Add {G} or {U}.

River Herald Guide

Vigilance
When River Herald Guide 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.)

Cenote Scout

When Cenote Scout 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.)

Forest

Entrancing Melody

Gain control of target creature with mana value X.

Nicanzil, Current Conductor

Whenever a creature you control explores a land card, you may put a land card from your hand onto the battlefield tapped.
Whenever a creature you control explores a nonland card, put a +1/+1 counter on Nicanzil, Current Conductor.

Jace, Ingenious Mind-Mage

+1: Draw a card.
+1: Untap all creatures you control.
−9: Gain control of up to three target creatures.

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.

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.

Crashing Tide

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

River Heralds' Boon

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

Tributary Instructor

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
Whenever a creature you control with a +1/+1 counter on it dies, draw a card.

Tempest Caller

When Tempest Caller enters, tap all creatures target opponent controls.

Jade Guardian

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

Island

Merfolk Mistbinder

River Sneak

River Sneak can't be blocked.
Whenever another Merfolk you control enters, River Sneak gets +1/+1 until end of turn.

Vineshaper Mystic

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

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Nezahal, Primal Tide

This spell can't be countered.
You have no maximum hand size.
Whenever an opponent casts a noncreature spell, draw a card.
Discard three cards: Exile Nezahal, Primal Tide. Return it to the battlefield tapped under its owner's control at the beginning of the next end step.