Grand Architect

Other blue creatures you control get +1/+1.
{U}: Target artifact creature becomes blue until end of turn.
Tap an untapped blue creature you control: Add {C}{C}. Spend this mana only to cast artifact spells or activate abilities of artifacts.

Vodalian Soldiers

Waterspout Weavers

Kinship — At the beginning of your upkeep, you may look at the top card of your library. If it shares a creature type with Waterspout Weavers, you may reveal it. If you do, each creature you control gains flying until end of turn.

Wanderwine Prophets

Champion a Merfolk (When this enters, sacrifice it unless you exile another Merfolk you control. When this leaves the battlefield, that card returns to the battlefield.)
Whenever Wanderwine Prophets deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.

Sunken City

At the beginning of your upkeep, sacrifice Sunken City unless you pay {U}{U}.
Blue creatures get +1/+1.

Summon the School

Create two 1/1 blue Merfolk Wizard creature tokens.
Tap four untapped Merfolk you control: Return Summon the School from your graveyard to your hand.

Merfolk of the Pearl Trident

Hollowsage

Whenever Hollowsage becomes untapped, you may have target player discard a card.

Rebuild

Return all artifacts to their owners' hands.
Cycling {2} ({2}, Discard this card: Draw a card.)

Hysterical Blindness

Creatures your opponents control get -4/-0 until end of turn.

Shoreline Raider

Inundate

Return all nonblue creatures to their owners' hands.

Merrow Reejerey

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

Gaea's Skyfolk

Lord of Atlantis

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

Coral Merfolk

Meekstone

Creatures with power 3 or greater don't untap during their controllers' untap steps.

Stonybrook Schoolmaster

Whenever Stonybrook Schoolmaster becomes tapped, you may create a 1/1 blue Merfolk Wizard creature token.

Riptide Pilferer

Whenever Riptide Pilferer deals combat damage to a player, that player discards a card.
Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Grand Abolisher

During your turn, your opponents can't cast spells or activate abilities of artifacts, creatures, or enchantments.

Inkfathom Infiltrator

Inkfathom Infiltrator can't block and can't be blocked.

Phyrexian Rebirth

Destroy all creatures, then create an X/X colorless Phyrexian Horror artifact creature token, where X is the number of creatures destroyed this way.

True Conviction

Creatures you control have double strike and lifelink.

Aura of Silence

Artifact and enchantment spells your opponents cast cost {2} more to cast.
Sacrifice Aura of Silence: Destroy target artifact or enchantment.

Merrow Witsniper

When Merrow Witsniper enters, target player mills a card.

Vodalian Zombie

Veteran of the Depths

Whenever Veteran of the Depths becomes tapped, you may put a +1/+1 counter on it.

Balance

Each player chooses a number of lands they control equal to the number of lands controlled by the player who controls the fewest, then sacrifices the rest. Players discard cards and sacrifice creatures the same way.

Cosi's Trickster

Whenever an opponent shuffles their library, you may put a +1/+1 counter on Cosi's Trickster.

Day of Judgment

Isolation Cell

Whenever an opponent casts a creature spell, that player loses 2 life unless they pay {2}.

Wake Thrasher

Whenever a permanent you control becomes untapped, Wake Thrasher gets +1/+1 until end of turn.

Rootwater Commando

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)