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.

Topsy Turvy

The phases of each player's turn are reversed. (The phases are, in reverse order, ending, second main, combat, first main, and beginning.)
As long as there are more than two players in the game, the turn order is reversed.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Graveyard Busybody

All graveyards are also your graveyards.
Graveyard Busybody's power and toughness are each equal to the number of cards with flavor text in your graveyards.

Swamp

Evil Twin

You may have Evil Twin enter as a copy of any creature on the battlefield, except it has "{U}{B}, {T}: Destroy target creature with the same name as this creature."

Basalt Monolith

Basalt Monolith doesn't untap during your untap step.
{T}: Add {C}{C}{C}.
{3}: Untap Basalt Monolith.

Phoebe, Head of S.N.E.A.K.

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.)

Ninja

You may activate Ninja's augment ability any time you could cast an instant.
Whenever this creature deals combat damage to a player,
Augment {2}{B} ({2}{B}, Reveal this card from your hand: Combine it with target host. Augment only as—oh, never mind.)

Arcane Signet

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

Jace Beleren

+2: Each player draws a card.
−1: Target player draws a card.
−10: Target player mills twenty cards.

Eye to Eye

You and target creature's controller have a staring contest. If you win, destroy that creature.

Charcoal Diamond

Charcoal Diamond enters tapped.
{T}: Add {B}.

Dark Tutelage

At the beginning of your upkeep, reveal the top card of your library and put that card into your hand. You lose life equal to its mana value.

Howling Mine

At the beginning of each player's draw step, if Howling Mine is untapped, that player draws an additional card.

Mastermind's Acquisition

Choose one —
• Search your library for a card, put it into your hand, then shuffle.
• Put a card you own from outside the game into your hand.

Warren Pilferers

When Warren Pilferers enters, return target creature card from your graveyard to your hand. If that card is a Goblin card, Warren Pilferers gains haste until end of turn.

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. Talisman of Dominance deals 1 damage to you.

Razaketh's Rite

Search your library for a card, put that card into your hand, then shuffle.
Cycling {B} ({B}, Discard this card: Draw a card.)

Mana Screw

{1}: Flip a coin. If you win the flip, add {C}{C}. Activate only as an instant.

Brainstorm

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

Mer Man

When this creature enters, you may draw a card.

Island

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Farewell to Arms

As Farewell to Arms enters, choose a hand attached to an opponent's arm.
When the chosen hand isn't behind its owner's back, sacrifice Farewell to Arms. If you do, that player discards their hand . . . of cards. (The lawyers wouldn't let us do it the other way.)

Mirror Mirror

Mirror Mirror enters tapped.
{7}, {T}, Sacrifice Mirror Mirror: Choose target player. At the beginning of the next end step, exchange life totals with that player, exchange control of all permanents you and that player control, and exchange cards in your hands, cards in your libraries, and cards in your graveyards.

Oversold Cemetery

At the beginning of your upkeep, if you have four or more creature cards in your graveyard, you may return target creature card from your graveyard to your hand.

Commander's Sphere

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

Otherworld Atlas

{T}: Put a charge counter on Otherworld Atlas.
{T}: Each player draws a card for each charge counter on Otherworld Atlas.

Sepulchral Primordial

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
When Sepulchral Primordial enters, for each opponent, you may put up to one target creature card from that player's graveyard onto the battlefield under your control.

Undertaker

{B}, {T}, Discard a card: Return target creature card from your graveyard to your hand.

Kill! Destroy!

Destroy target nonblack creature.
Gotcha — If an opponent says "kill" or "destroy," you may say "Gotcha!" When you do, return Kill! Destroy! from your graveyard to your hand.

Clocknapper

When Clocknapper enters, choose beginning phase, first main phase, combat phase, postcombat main phase, or ending phase. Steal that phase from target player during their next turn. (That phase occurs as though it's your turn instead.)

Sky Diamond

Dimir Guildgate

This land enters tapped.
{T}: Add {U} or {B}.

Thought Vessel

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

Whispersilk Cloak

Equipped creature can't be blocked and has shroud. (It can't be the target of spells or abilities.)
Equip {2}

Robo-

At the beginning of each end step, if an artifact entered the battlefield under your control this turn,
Augment {2} ({2}, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)

Dimir Signet

Rune-Scarred Demon

Flying
When this creature enters, search your library for a card, put it into your hand, then shuffle.

Rings a Bell

As Rings a Bell enters, choose a word with four or more letters.
After you say the chosen word for the first time each turn, an opponent may ring or imitate a bell within five seconds. When no opponent does, draw a card.

Half-Shark, Half-

At the beginning of your upkeep,
Augment {5}{U} ({5}{U}, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)

Loose Lips

Enchant creature
As Loose Lips enters, choose a sentence with eight or fewer words.
Enchanted creature has flying.
Whenever enchanted creature deals damage to an opponent, that player may say the chosen sentence. If they don't, you draw two cards.

Clever Impersonator

You may have Clever Impersonator enter as a copy of any nonland permanent on the battlefield.

Angelic Rocket

Flying
When this creature enters, you may destroy target nonland permanent.

Border Guardian

Whenever you cast a silver-bordered spell, put a +1/+1 counter on Border Guardian.
Whenever you cast a black-bordered spell, Border Guardian can't be blocked this turn.
Whenever you cast a white-bordered spell, Border Guardian gains double strike until end of turn.

Steam-Powered

{5}:
Augment {4} ({4}, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)

Sly Spy

Whenever Sly Spy deals combat damage to a player, you may destroy target creature facing left in its art. (Creatures without faces don't face anywhere.)

Johnny, Combo Player

{4}: Search your library for a card, put that card into your hand, then shuffle.

Rise from the Grave

Put target creature card from a graveyard onto the battlefield under your control. That creature is a black Zombie in addition to its other colors and types.

Gravedigger

When Gravedigger enters, you may return target creature card from your graveyard to your hand.

Mirage Mirror

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

Censorship

As Censorship enters, choose a word.
Whenever a player says the chosen word, Censorship deals 2 damage to that player.

Mikokoro, Center of the Sea

{T}: Add {C}.
{2}, {T}: Each player draws a card.

Entirely Normal Armchair

During your turn, if Entirely Normal Armchair is in your hand, you may hide it on the battlefield.
{0}: Return Entirely Normal Armchair to its owner's hand. Only your opponents may activate this ability and only if they see Entirely Normal Armchair.
{2}, Sacrifice Entirely Normal Armchair: Destroy target attacking creature.

The Big Top

{T}: Add one mana of any color that appears on your top. (A top is an outerwear garment worn on the upper body.)

Body Double

You may have Body Double enter as a copy of any creature card in a graveyard.

Over My Dead Bodies

Creature cards in graveyards can attack and block as though they were on the battlefield, can block or be blocked only by creature cards in graveyards, are Zombies in addition to their other types, and have undeathtouch. (If they would deal damage to a creature card, exile that creature card instead.)
Creature cards in your graveyard have haste.

Animate Library

Enchant your library
Enchanted library is an artifact creature on the battlefield with power and toughness each equal to the number of cards in it. It's still a library.
If enchanted library would leave the battlefield, exile Animate Library instead.

Dismal Backwater

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {B}.

Masterful Ninja

Haste
Reveal Masterful Ninja from your hand: Masterful Ninja is on the battlefield and in your hand until end of turn.
{1}{B}: Masterful Ninja gets +1/+1 until end of turn.

Submerged Boneyard

Submerged Boneyard enters tapped.
{T}: Add {U} or {B}.

Darksteel Ingot

Indestructible (Effects that say "destroy" don't destroy this artifact.)
{T}: Add one mana of any color.

Clone

You may have Clone enter as a copy of any creature on the battlefield.

Duskmantle Seer

Flying
At the beginning of your upkeep, each player reveals the top card of their library, loses life equal to that card's mana value, then puts it into their hand.

Jwar Isle Refuge

Jwar Isle Refuge enters tapped.
When Jwar Isle Refuge enters, you gain 1 life.
{T}: Add {U} or {B}.

Consuming Aberration

Consuming Aberration's power and toughness are each equal to the number of cards in your opponents' graveyards.
Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

World-Bottling Kit

{5}, Sacrifice World-Bottling Kit: Choose a Magic set. Exile all permanents with that set's expansion symbol except for basic lands.

Nighteyes the Desecrator

{4}{B}: Put target creature card from a graveyard onto the battlefield under your control.

Nezumi Graverobber

{1}{B}: Exile target card from an opponent's graveyard. If no cards are in that graveyard, flip Nezumi Graverobber.

Nezumi Graverobber // Nighteyes the Desecrator

Grafted Wargear

Equipped creature gets +3/+2.
Whenever Grafted Wargear becomes unattached from a permanent, sacrifice that permanent.
Equip {0} ({0}: Attach to target creature you control. Equip only as a sorcery.)

Destroy target creature with reminder text. (Reminder text is any italicized text in parentheses that explains rules you already know.)

Big Boa Constrictor

When this creature enters, roll a six-sided die. Target opponent loses life equal to the result.

Vislor Turlough

Deal with the Black Guardian — When Vislor Turlough enters, you may have an opponent gain control of it. If you do, it's goaded for as long as they control it.
At the beginning of your end step, draw a card, then you lose life equal to the number of cards in your hand.
Doctor's companion (You can have two commanders if the other is the Doctor.)

Well of Knowledge

{2}: Draw a card. Any player may activate this ability but only during their draw step.

Underdome

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to pay Un-costs.

Split Screen

When Split Screen enters, shuffle your library and deal it into four libraries. If anything refers to your library, choose one of your libraries for it.
Play with your libraries' top cards revealed.
When Split Screen leaves the battlefield, shuffle your libraries together.

Dimir Doppelganger

{1}{U}{B}: Exile target creature card from a graveyard. Dimir Doppelganger becomes a copy of that card, except it has this ability.

Temple Bell

Puppeteer Clique

Flying
When Puppeteer Clique enters, put target creature card from an opponent's graveyard onto the battlefield under your control. It gains haste. At the beginning of your next end step, exile it.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Tortured Existence

{B}, Discard a creature card: Return target creature card from your graveyard to your hand.

Magical Hacker

{U}: Change the text of target spell or permanent by replacing all instances of + with -, and vice versa, until end of turn.

Diabolic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Dirty Rat

When this creature enters, target opponent discards a card.

Spy Eye

Flying
Whenever Spy Eye deals combat damage to a player, you may draw a card from that player's library.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Zombified

{4}{B}: Combine Zombified from your graveyard with target host.
{2}{B}, Exile a creature card from your graveyard:
Augment {4}{B} ({4}{B}, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)

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}.