Skyblade's Boon

Enchant creature
Enchanted creature gets +1/+1 and has flying.
{2}{W}: Return Skyblade's Boon to its owner's hand. Activate only if Skyblade's Boon is on the battlefield or in your graveyard.

Merfolk Looter

Island

Merfolk Windrobber

Flying
Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. (They put the top card of their library into their graveyard.)
Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.

Wishful Merfolk

Defender
{1}{U}: Wishful Merfolk loses defender and becomes a Human until end of turn.

Merfolk Sovereign

Other Merfolk creatures you control get +1/+1.
{T}: Target Merfolk creature can't be blocked this turn.

Sky Crier

Flying, lifelink
{3}{W}: You and target opponent each draw a card.

Skycloud Expanse

Skyreach Manta

Sunburst (This enters the battlefield with a +1/+1 counter on it for each color of mana spent to cast it.)
Flying

Kairi, the Swirling Sky

Flying, ward {3}
When Kairi, the Swirling Sky dies, choose one —
• Return any number of target nonland permanents with total mana value 6 or less to their owners' hands.
• Mill six cards, then return up to two instant and/or sorcery cards from your graveyard to your hand.

Coral Merfolk

Skyline Cascade

Skyline Cascade enters the battlefield tapped.
When Skyline Cascade enters the battlefield, target creature an opponent controls doesn't untap during its controller's next untap step.
{T}: Add {U}.

Abzan Skycaptain

Flying
When Abzan Skycaptain dies, bolster 2. (Choose a creature with the least toughness among creatures you control and put two +1/+1 counters on it.)

Kangee, Sky Warden

Flying, vigilance
Whenever Kangee, Sky Warden attacks, attacking creatures with flying get +2/+0 until end of turn.
Whenever Kangee blocks, blocking creatures with flying get +0/+2 until end of turn.

Merfolk Falconer

Flying
Whenever you cast a kicked spell, scry 2.

Sky Diamond

Sky Diamond enters the battlefield tapped.
{T}: Add {U}.

Coralhelm Commander

Level up {1} ({1}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 2-3
3/3
Flying
LEVEL 4+
4/4
Flying
Other Merfolk creatures you control get +1/+1.

Maul of the Skyclaves

When Maul of the Skyclaves enters the battlefield, attach it to target creature you control.
Equipped creature gets +2/+2 and has flying and first strike.
Equip {2}{W}{W}

Skybridge Towers

Skybridge Towers enters the battlefield tapped.
{T}: Add {W} or {U}.
{2}{W}{U}, {T}, Sacrifice Skybridge Towers: Draw a card.

Long-Finned Skywhale

Flying
Long-Finned Skywhale can block only creatures with flying.

Merfolk Skyscout

Flying
Whenever Merfolk Skyscout attacks or blocks, untap target permanent.

Merfolk of the Pearl Trident

Skyclave Plunder

Look at the top X cards of your library, where X is three plus the number of creatures in your party. Put three of those cards into your hand and the rest on the bottom of your library in a random order. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)

Skyboon Evangelist

Flying
When Skyboon Evangelist enters the battlefield, support 6. (Put a +1/+1 counter on each of up to six other target creatures.)
Whenever a creature with a counter on it attacks one of your opponents, that creature gains flying until end of turn.

Merfolk Spy

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Merfolk Spy deals combat damage to a player, that player reveals a card at random from their hand.

Skymark Roc

Flying
Whenever Skymark Roc attacks, you may return target creature defending player controls with toughness 2 or less to its owner's hand.

Blue Dragon

Flying
Lightning Breath — When Blue Dragon enters the battlefield, until your next turn, target creature an opponent controls gets -3/-0, up to one other target creature gets -2/-0, and up to one other target creature gets -1/-0.

Dance of the Skywise

Until end of turn, target creature you control becomes a blue Dragon Illusion with base power and toughness 4/4, loses all abilities, and gains flying.

Shabraz, the Skyshark

Partner with Brallin, Skyshark Rider
Flying
Whenever you draw a card, put a +1/+1 counter on Shabraz, the Skyshark and you gain 1 life.
{W/U}: Target Human gains flying until end of turn.

Seller of Songbirds

When Seller of Songbirds enters the battlefield, create a 1/1 white Bird creature token with flying.

Mystic Skyfish

Whenever you draw your second card each turn, Mystic Skyfish gains flying until end of turn.

Skyreaping

Skyreaping deals damage to each creature with flying equal to your devotion to green. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)

Plains

Gray Harbor Merfolk

Gray Harbor Merfolk can't be blocked.
Gray Harbor Merfolk gets +2/+0 as long as you control a commander that's a creature or planeswalker.

Mu Yanling, Sky Dancer

+2: Until your next turn, up to one target creature gets -2/-0 and loses flying.
−3: Create a 4/4 blue Elemental Bird creature token with flying.
−8: You get an emblem with "Islands you control have '{T}: Draw a card.'"

Pristine Skywise

Flying
Whenever you cast a noncreature spell, untap Pristine Skywise. It gains protection from the color of your choice until end of turn.

Merfolk Trickster

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

Enchant creature
Enchanted creature has flying and "Whenever this creature deals combat damage to a player, venture into the dungeon." (Enter the first room or advance to the next room.)

Merfolk Observer

When Merfolk Observer enters the battlefield, look at the top card of target player's library.

Sky-Eel School

Flying
When Sky-Eel School enters the battlefield, draw a card, then discard a card.

Merfolk Wayfinder

Flying
When Merfolk Wayfinder enters the battlefield, reveal the top three cards of your library. Put all Island cards revealed this way into your hand and the rest on the bottom of your library in any order.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.