Judge of Currents

Whenever a Merfolk you control becomes tapped, you may gain 1 life.

Lullmage Mentor

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token.
Tap seven untapped Merfolk you control: Counter target spell.

Vodalian Hexcatcher

Flash
Other Merfolk you control get +1/+1.
Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

Faces of the Past

Whenever a creature dies, tap all untapped creatures that share a creature type with it or untap all tapped creatures that share a creature type with it.

Thieving Skydiver

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)
Flying
When this creature enters, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to this creature.

Merrow Commerce

At the beginning of your end step, untap all Merfolk you control.

Stonybrook Schoolmaster

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

Zur the Enchanter

Flying
Whenever Zur attacks, you may search your library for an enchantment card with mana value 3 or less, put it onto the battlefield, then shuffle.

Crashing Drawbridge

Defender
{T}: Creatures you control gain haste until end of turn.

Sygg, River Cutthroat

At the beginning of each end step, if an opponent lost 3 or more life this turn, you may draw a card. (Damage causes loss of life.)

Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters, untap all creatures.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Merfolk Trickster

Flash
When this creature enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Fallowsage

Whenever this creature becomes tapped, you may draw a card.

Sigil Tracer

{1}{U}, Tap two untapped Wizards you control: Copy target instant or sorcery spell. You may choose new targets for the copy.

Caetus, Sea Tyrant of Segovia

Noncreature spells you cast have convoke. (Your creatures can help cast those spells. Each creature you tap while casting a noncreature spell pays for {1} or one mana of that creature's color.)
At the beginning of your end step, untap up to four target creatures.

Invasion of Segovia

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When this Siege enters, create two 1/1 blue Kraken creature tokens with trample.

Invasion of Segovia // Caetus, Sea Tyrant of Segovia

Dress Down

Flash
When this enchantment enters, draw a card.
Creatures lose all abilities.
At the beginning of the end step, sacrifice this enchantment.

Mirrorweave

Each other creature becomes a copy of target nonlegendary creature until end of turn.

Cursecatcher

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

Surgespanner

Whenever this creature becomes tapped, you may pay {1}{U}. If you do, return target permanent to its owner's hand.