Riverguard's Reflexes

Target creature gets +2/+2 and gains first strike until end of turn. Untap it.

Wanderbrine Preacher

Whenever this creature becomes tapped, you gain 2 life.

Deepchannel Duelist

At the beginning of your end step, untap target Merfolk you control.
Other Merfolk you control get +1/+1.

Plains

Blossombind

Enchant creature
When this Aura enters, tap enchanted creature.
Enchanted creature can't become untapped and can't have counters put on it.

Merrow Skyswimmer

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Flying, vigilance
When this creature enters, create a 1/1 white and blue Merfolk creature token.

Temporal Cleansing

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
The owner of target nonland permanent puts it into their library second from the top or on the bottom.

Island

Thirst for Identity

Draw three cards. Then discard two cards unless you discard a creature card.

Sygg's Command

Choose two —
• Create a token that's a copy of target Merfolk you control.
• Creatures target player controls gain lifelink until end of turn.
• Target player draws a card.
• Tap target creature. Put a stun counter on it.

Aquitect's Defenses

Flash
Enchant creature you control
When this Aura enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+2.

Liminal Hold

When this enchantment enters, exile up to one target nonland permanent an opponent controls until this enchantment leaves the battlefield. You gain 2 life.

Tributary Vaulter

Flying
Whenever this creature becomes tapped, another target Merfolk you control gets +2/+0 until end of turn.

Evolving Wilds

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Deepway Navigator

Flash
When this creature enters, untap each other Merfolk you control.
As long as you attacked with three or more Merfolk this turn, Merfolk you control get +1/+0.

Silvergill Peddler

Whenever this creature becomes tapped, draw a card, then discard a card.

Appeal to Eirdu

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
One or two target creatures each get +2/+1 until end of turn.