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.

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

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

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.

{T}: Add {C}.

{1}, {T}: Until end of turn, creatures your opponents control lose hexproof and shroud and can't have hexproof or shroud.

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

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

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

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.

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

You may choose not to untap Callous Oppressor during your untap step.

As Callous Oppressor enters the battlefield, an opponent chooses a creature type.

{T}: Gain control of target creature that isn't of the chosen type for as long as Callous Oppressor remains tapped.

Enchant creature

You control enchanted creature.

You may have Copy Enchantment enter the battlefield as a copy of any enchantment on the battlefield.

Counter target spell.

When Court of Vantress enters the battlefield, you become the monarch.

At the beginning of your upkeep, choose up to one other target enchantment or artifact. If you're the monarch, you may create a token that's a copy of it. If you're not the monarch, you may have Court of Vantress become a copy of it, except it has this ability.

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

Whenever one or more nontoken Merfolk you control become tapped, create a 1/1 blue Merfolk creature token with hexproof.

Whenever you cast a Merfolk spell, create a 1/1 blue Merfolk creature token with hexproof. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

Flying

As an additional cost to cast blue permanent spells, you may pay 2 life. Those spells cost {U} less to cast if you paid life this way. This effect reduces only the amount of blue mana you pay.

Whenever you cast a blue permanent spell, draw a card.

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

Enchant permanent

You can't choose an untapped permanent as this spell's target as you cast it.

You control enchanted permanent.

Tap an untapped Merfolk you control: Target player mills a card.

{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.)

You may look at the top card of your library any time.

You may cast Merfolk spells from the top of your library.

Whenever you cast a Merfolk spell, you may pay {1}. If you do, create a 1/1 blue Merfolk creature token.

{U}{U}, {T}: Gain control of target legendary permanent. (This effect lasts indefinitely.)

You may have Estrid's Invocation enter the battlefield as a copy of an enchantment you control, except it has "At the beginning of your upkeep, you may exile this enchantment. If you do, return it to the battlefield under its owner's control."

Enchant creature

When enchanted creature dies, return that card to the battlefield under your control.

When Fool's Demise is put into a graveyard from the battlefield, return Fool's Demise to its owner's hand.

Guile can't be blocked except by three or more creatures.

If a spell or ability you control would counter a spell, instead exile that spell and you may play that card without paying its mana cost.

When Guile is put into a graveyard from anywhere, shuffle it into its owner's library.

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)

When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

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

Whenever an ability of equipped creature is activated, if it isn't a mana ability, copy that ability. You may choose new targets for the copy.

Equip {3}

Suspend 3--{1}{U}{U} (Rather than cast this card from your hand, pay {1}{U}{U} and exile it with three time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, cast it without paying its mana cost.)

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

Gain control of target artifact or creature. Untap it.

Spells your opponents cast that target a Merfolk you control cost {2} more to cast.

Abilities your opponents activate that target a Merfolk you control cost {2} more to activate.

If Leyline of Anticipation is in your opening hand, you may begin the game with it on the battlefield.

You may cast spells as though they had flash.

If Leyline of Singularity is in your opening hand, you may begin the game with it on the battlefield.

All nonland permanents are legendary.

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

Equip {0}

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.

{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.)

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

Other Merfolk creatures you control get +1/+1.

{T}: Target Merfolk creature can't be blocked this turn.

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

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

When Merrow Harbinger enters the battlefield, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.

Other Merfolk creatures you control get +1/+1.

Whenever you cast a Merfolk spell, you may tap or untap target permanent.

{T}: Add {U}.

{U}, {T}: Untap target legendary permanent.

Whenever an opponent casts their first spell each turn, that player exiles the top card of their library. If it's a nonland card, you may cast it without paying its mana cost.

{T}: Add one mana of any color.

{1}, {T}: Untap target legendary creature you control.

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

You have no maximum hand size.

{T}: Add {C}.

Whenever Riptide Entrancer deals combat damage to a player, you may sacrifice it. If you do, gain control of target creature that player controls. (This effect lasts indefinitely.)

Morph {U}{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.)

Flying

Landfall -- Whenever a land enters the battlefield under your control, you may gain control of target creature for as long as you control Roil Elemental.

{T}: Rootwater Hunter deals 1 damage to any target.

{T}: Gain control of target creature for as long as that creature is enchanted.

You may cast Aura spells with enchant creature as though they had flash.

Blue spells you cast cost {1} less to cast.

Flying

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

{T}: Add {C}{C}.

When Solemn Simulacrum enters the battlefield, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

When Solemn Simulacrum dies, you may draw a card.

Flying

When Sower of Temptation enters the battlefield, gain control of target creature for as long as Sower of Temptation remains on the battlefield.

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

Merfolk spells and Wizard spells you cast cost {1} less to cast.

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

Svyelun of Sea and Sky has indestructible as long as you control at least two other Merfolk.

Whenever Svyelun attacks, draw a card.

Other Merfolk you control have ward {1}. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)

Equip {1}

Whenever you cast an instant or sorcery spell, create a 2/2 blue Drake creature token with flying.

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

Whenever Thada Adel, Acquisitor deals combat damage to a player, search that player's library for an artifact card and exile it. Then that player shuffles. Until end of turn, you may play that card.

Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

You have no maximum hand size.

{T}: Add {C}.

You may activate abilities of creatures you control as though those creatures had haste.

{1}, {T}: Untap target creature.

When Tolarian Contempt enters the battlefield, put a rejection counter on each creature your opponents control.

At the beginning of your end step, for each opponent, choose up to one target creature they control with a rejection counter on it. That creature's owner puts it on the top or bottom of their library.

Whenever Tolarian Entrancer becomes blocked by a creature, gain control of that creature at end of combat.

You may choose not to untap Vedalken Shackles during your untap step.

{2}, {T}: Gain control of target creature with power less than or equal to the number of Islands you control for as long as Vedalken Shackles remains tapped.

Flash

Other Merfolk you control get +1/+1.

Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

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