Extract Brain

Target opponent chooses X cards from their hand. Look at those cards. You may cast a spell from among them without paying its mana cost.

Undermine

Counter target spell. Its controller loses 3 life.

Subjugate the Hobbits

Gain control of each noncommander creature with mana value 3 or less.

Siren of the Silent Song

Flying
Inspired — Whenever Siren of the Silent Song becomes untapped, each opponent discards a card, then each opponent mills a card.

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Infernal Grasp

Destroy target creature. You lose 2 life.

Swamp

Beguiler of Wills

{T}: Gain control of target creature with power less than or equal to the number of creatures you control.

Threnody Singer

Flash
Flying
When Threnody Singer enters the battlefield, target creature an opponent controls gets -X/-0 until end of turn, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Sol Ring

Dispel

Agent of Treachery

When Agent of Treachery enters the battlefield, gain control of target permanent.
At the beginning of your end step, if you control three or more permanents you don't own, draw three cards.

Watery Grave

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

Island

Vohar, Vodalian Desecrator

{T}: Draw a card, then discard a card. If you discarded an instant or sorcery card this way, each opponent loses 1 life and you gain 1 life.
{2}, Sacrifice Vohar, Vodalian Desecrator: You may cast target instant or sorcery card from your graveyard this turn. If that spell would be put into your graveyard, exile it instead. Activate only as a sorcery.

Memory Plunder

You may cast target instant or sorcery card from an opponent's graveyard without paying its mana cost.

Sunken Hollow

({T}: Add {U} or {B}.)
Sunken Hollow enters the battlefield tapped unless you control two or more basic lands.

Thief of Sanity

Flying
Whenever Thief of Sanity deals combat damage to a player, look at the top three cards of that player's library, exile one of them face down, then put the rest into their graveyard. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.

Stroke of Genius

Commander's Sphere

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

Hypnotic Siren

Bestow {5}{U}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Flying
You control enchanted creature.
Enchanted creature gets +1/+1 and has flying.

Bribery

Search target opponent's library for a creature card and put that card onto the battlefield under your control. Then that player shuffles.

Pull from Tomorrow

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Siren of the Fanged Coast

Flying
Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Siren of the Fanged Coast enters the battlefield, if tribute wasn't paid, gain control of target creature.

Dominate

Gain control of target creature with mana value X or less.

Dulcet Sirens

{U}, {T}: Target creature attacks target opponent this turn if able.
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.)

Countersquall

Counter target noncreature spell. Its controller loses 2 life.

Siren Lookout

Flying
When Siren Lookout enters the battlefield, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Force of Negation

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.

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Sunken Ruins

{T}: Add {C}.
{U/B}, {T}: Add {U}{U}, {U}{B}, or {B}{B}.

Soul Manipulation

Choose one or both —
• Counter target creature spell.
• Return target creature card from your graveyard to your hand.

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Dreadship Reef

{T}: Add {C}.
{1}, {T}: Put a storage counter on Dreadship Reef.
{1}, Remove X storage counters from Dreadship Reef: Add X mana in any combination of {U} and/or {B}.

Mistral Singer

Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Blue Sun's Twilight

Gain control of target creature with mana value X or less. If X is 5 or more, create a token that's a copy of that creature.

Control Magic

Enchant creature
You control enchanted creature.

Perplex

Counter target spell unless its controller discards their hand.
Transmute {1}{U}{B} ({1}{U}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Confiscate

Enchant permanent
You control enchanted permanent.

Zephyr Singer

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Flying, vigilance
When Zephyr Singer enters the battlefield, put a flying counter on each creature that convoked it.

Araumi of the Dead Tide

{T}, Exile cards from your graveyard equal to the number of opponents you have: Target creature card in your graveyard gains encore until end of turn. The encore cost is equal to its mana cost. (Exile the creature card and pay its mana cost: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Mass Manipulation

Gain control of X target creatures and/or planeswalkers.

Blatant Thievery

For each opponent, gain control of target permanent that player controls.

Concoct

Surveil 3, then return a creature card from your graveyard to the battlefield.

Connive

Gain control of target creature with power 2 or less.

Connive // Concoct

Drown in the Loch

Choose one —
• Counter target spell with mana value less than or equal to the number of cards in its controller's graveyard.
• Destroy target creature with mana value less than or equal to the number of cards in its controller's graveyard.

Propaganda

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Maeve, Insidious Singer

{2}{U}: Goad target creature. Whenever that creature attacks one of your opponents this turn, you draw a card. (A goaded creature attacks each combat if able and attacks a player other than you if able, until your next turn.)

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Malcolm, Alluring Scoundrel

Flash
Flying
Whenever Malcolm, Alluring Scoundrel deals combat damage to a player, put a chorus counter on it. Draw a card, then discard a card. If there are four or more chorus counters on Malcolm, you may cast the discarded card without paying its mana cost.

Mind Control

Arcane Signet

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Dramatic Reversal

Untap all nonland permanents you control.

Condescend

Counter target spell unless its controller pays {X}. Scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Blue Sun's Zenith

Target player draws X cards. Shuffle Blue Sun's Zenith into its owner's library.

Negate

Dimir Signet

Siren Stormtamer

Flying
{U}, Sacrifice Siren Stormtamer: Counter target spell or ability that targets you or a creature you control.

Patriar's Seal

{T}: Add one mana of any color.
{1}, {T}: Untap target legendary creature you control.

Cyclonic Rift

Return target nonland permanent you don't control to its owner's hand.
Overload {6}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Thought Vessel

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Covetous Urge

Target opponent reveals their hand. You choose a nonland card from that player's graveyard or hand and exile it. You may cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell.

Alluring Siren

{T}: Target creature an opponent controls attacks you this turn if able.

Aethersnatch

Gain control of target spell. You may choose new targets for it. (If that spell becomes a permanent, it enters the battlefield under your control.)

Nyx Lotus

Nyx Lotus enters the battlefield tapped.
{T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Dreamcaller Siren

Flash
Flying
Dreamcaller Siren can block only creatures with flying.
When Dreamcaller Siren enters the battlefield, if you control another Pirate, tap up to two target nonland permanents.

Thassa, God of the Sea

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
At the beginning of your upkeep, scry 1.
{1}{U}: Target creature you control can't be blocked this turn.

Force of Will

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost.
Counter target spell.

Counterspell

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Shipwreck Singer

Flying
{1}{U}: Target creature an opponent controls attacks this turn if able.
{1}{B}, {T}: Attacking creatures get -1/-1 until end of turn.