Exile target attacking creature. Then remove it from the game. Then put it into the absolutely-removed-from-the-freaking-game-forever zone.

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.

+1: Create a 2/3 blue and black Nightmare creature token with "Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library."

-3: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.

-7: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.

+2: Exile the top three cards of target opponent's library.

-X: Put a creature card with mana value X exiled with Ashiok, Nightmare Weaver onto the battlefield under your control. That creature is a Nightmare in addition to its other types.

-10: Exile all cards from all opponents' hands and graveyards.

+2: Draw a card. Each player mills two cards.

-5: Put target creature card from a graveyard onto the battlefield under your control.

-11: Gain control of all creatures target opponent 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.

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

At the beginning of your upkeep, exile the top card of target opponent's library. You may play that card for as long as it remains exiled, and mana of any type can be spent to cast it. If you're the monarch, until end of turn, you may cast a spell from among cards exiled with Court of Locthwain without paying its mana cost.

At the beginning of your upkeep, you may ask target player a yes-or-no question. If you do, that player answers the question truthfully and abides by that answer if able until end of turn.

When GO TO JAIL enters the battlefield, exile target creature an opponent controls until GO TO JAIL leaves the battlefield.

At the beginning of the upkeep of the exiled card's owner, that player rolls two six-sided dice. If they roll doubles, sacrifice GO TO JAIL.

When Hostage Taker enters the battlefield, exile another target creature or artifact until Hostage Taker leaves the battlefield. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.

{2}: Mirage Mirror becomes a copy of target artifact, creature, enchantment, or land until end of turn.

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Counter target noncreature spell. Your opponents can't cast noncreature spells this turn.

Phoebe, Head of S.N.E.A.K. can't be blocked by creatures with flavor text.

{2}{U}{B}: Phoebe permanently steals target creature's text box. (That creature loses all rules text, flavor text, and watermarks. This creature gains them.)

Ward--Discard an enchantment, instant, or sorcery card.

Whenever you cast your second spell each turn, each opponent mills two cards. When one or more cards are milled this way, exile target enchantment, instant, or sorcery card with equal or lesser mana value than that spell from an opponent's graveyard. Copy the exiled card. You may cast the copy without paying its mana cost.

At the beginning of your upkeep, choose target opponent. This turn, that player can't cast spells or activate abilities and plays with their hand revealed. You may play lands and cast spells from that player's hand this turn.

Exile target creature. Its controller gains life equal to its power.

Whenever you cast a spell you don't own, create a 3/3 black Demon creature token.

+1: Draw a card. For each opponent, exile up to one target instant or sorcery card from that player's graveyard and put a page counter on it.

-3: You may cast a spell from among cards in exile with page counters on them without paying its mana cost.

Tasha, the Witch Queen can be your commander.

Your opponents play with their hands revealed.

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 it.

As long as X is in X's owner's opponent's hand, X's owner may cast X and activate X's abilities. That opponent can't cast X and plays with their hand revealed.

{U}{B}, {T}: Put X into target opponent's hand.

{3}{U}{B}: You may play a land or cast a spell from the hand X is in. If you cast a spell this way, you cast it without paying its mana cost.

At the beginning of your upkeep, choose target opponent. Until end of turn, that player can't cast spells, you may look at the top card of their library any time, you may play the top card of their library, and you may spend mana as though it were mana of any color to cast spells this way.