Gravelgill Duo

Whenever you cast a blue spell, Gravelgill Duo gets +1/+1 until end of turn.
Whenever you cast a black spell, Gravelgill Duo gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)

Oona, Queen of the Fae

Flying
{X}{U/B}: Choose a color. Target opponent exiles the top X cards of their library. For each card of the chosen color exiled this way, create a 1/1 blue and black Faerie Rogue creature token with flying.

Silkbind Faerie

Flying
{1}{W/U}, {Q}: Tap target creature. ({Q} is the untap symbol.)

Thistledown Duo

Whenever you cast a white spell, Thistledown Duo gets +1/+1 until end of turn.
Whenever you cast a blue spell, Thistledown Duo gains flying until end of turn.

Advice from the Fae

({2/U} can be paid with any two mana or with {U}. This card's mana value is 6.)
Look at the top five cards of your library. If you control more creatures than each other player, put two of those cards into your hand. Otherwise, put one of them into your hand. Then put the rest on the bottom of your library in any order.

Spell Syphon

Counter target spell unless its controller pays {1} for each blue permanent you control.

Helm of the Ghastlord

Enchant creature
As long as enchanted creature is blue, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, draw a card."
As long as enchanted creature is black, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, that player discards a card."

Swamp

Loch Korrigan

{U/B}: Loch Korrigan gets +1/+1 until end of turn.

Somnomancer

When Somnomancer enters, you may tap target creature.

Traitor's Roar

Tap target untapped creature. It deals damage equal to its power to its controller.
Conspire (As you cast this spell, you may tap two untapped creatures you control that share a color with it. When you do, copy it and you may choose a new target for the copy.)

Turn to Mist

Exile target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Island

Kinscaer Harpoonist

Flying
Whenever Kinscaer Harpoonist attacks, you may have target creature lose flying until end of turn.

Briarberry Cohort

Flying
Briarberry Cohort gets +1/+1 as long as you control another blue creature.

Leech Bonder

Leech Bonder enters with two -1/-1 counters on it.
{U}, {Q}: Move a counter from target creature onto a second target creature. ({Q} is the untap symbol.)

Aethertow

Put target attacking or blocking creature on top of its owner's library.
Conspire (As you cast this spell, you may tap two untapped creatures you control that share a color with it. When you do, copy it and you may choose a new target for the copy.)

Fate Transfer

Move all counters from target creature onto another target creature.

Inkfathom Witch

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
{2}{U}{B}: Each unblocked creature has base power and toughness 4/1 until end of turn.

River's Grasp

If {U} was spent to cast this spell, return up to one target creature to its owner's hand. If {B} was spent to cast this spell, target player reveals their hand, you choose a nonland card from it, then that player discards that card. (Do both if {U}{B} was spent.)