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.)

River Sneak

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

Jade Bearer

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

Watertrap Weaver

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

Jace, Ingenious Mind-Mage

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

Merfolk Branchwalker

When Merfolk Branchwalker 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.)

Forerunner of the Heralds

When Forerunner of the Heralds enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.
Whenever another Merfolk you control enters, put a +1/+1 counter on Forerunner of the Heralds.

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.

Shaper Apprentice

Shaper Apprentice has flying as long as you control another Merfolk.

Tempest Caller

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

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.

Woodland Stream

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

Seafloor Oracle

Whenever a Merfolk you control deals combat damage to a player, draw a card.

Waterknot

Enchant creature
When Waterknot enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Island

Slice in Twain

Destroy target artifact or enchantment.
Draw a card.

Merfolk Mistbinder

Forest

Silvergill Adept

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters, draw a card.

Vineshaper Mystic

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

Jadelight Ranger

When Jadelight Ranger enters, it explores, then it explores again. (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. Then repeat this process.)