Sacrifice Cursecatcher: Counter target instant or sorcery spell unless its controller pays {1}.

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Other Merfolk creatures you control get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Flash When Merfolk Trickster enters the battlefield, tap target creature an opponent controls. It loses all abilities until end of turn.

Other Merfolk creatures you control get +1/+1. Whenever you cast a Merfolk spell, you may tap or untap target permanent.

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

Svyelun of Sea and Sky has indestructible as long as you control at least two other Merfolk. Whenever Svyelun attacks, draw a card. Other Merfolk you control have ward {1}. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

({T}: Add {G} or {U}.) As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

({T}: Add {W} or {U}.) As Hallowed Fountain enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

{T}, Pay 1 life, Sacrifice Misty Rainforest: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

{T}: Add {C}. {1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Seachrome Coast enters the battlefield tapped unless you control two or fewer other lands. {T}: Add {W} or {U}.

({T}: Add {U}.)

At the beginning of your upkeep, you may put a charge counter on Aether Vial. {T}: You may put a creature card with mana value equal to the number of charge counters on Aether Vial from your hand onto the battlefield.

Chalice of the Void enters the battlefield with X charge counters on it. Whenever a player casts a spell with mana value equal to the number of charge counters on Chalice of the Void, counter that spell.

Chalice of the Void enters the battlefield with X charge counters on it. Whenever a player casts a spell with mana value equal to the number of charge counters on Chalice of the Void, counter that spell.

If it's not your turn, you may exile a blue card from your hand rather than pay this spell's mana cost. Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.) When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Sacrifice Mistcaller: Until end of turn, if a nontoken creature would enter the battlefield and it wasn't cast, exile it instead.

Converge — Exile target nonland permanent if its mana value is less than or equal to the number of colors of mana spent to cast this spell.

{T}: Target player exiles a card from their graveyard. {1}, Exile Relic of Progenitus: Exile all graveyards. Draw a card.