Arvinox, the Mind Flail isn't a creature unless you control three or more permanents you don't own.

At the beginning of your end step, exile the bottom card of each opponent's library face down. For as long as those cards remain exiled, you may look at them, you may cast permanent spells from among them, and you may spend mana as though it were mana of any color to cast those spells.

+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.

Flying, deathtouch

When Baleful Strix enters, draw a card.

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

Protection from green (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything green.)

Creatures your opponents control can't have +1/+1 counters put on them.

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.

Flying

At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.

Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.

If an opponent would mill one or more cards, they mill twice that many cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

Castle Vantress enters the battlefield tapped unless you control an Island.

{T}: Add {U}.

{2}{U}{U}, {T}: Scry 2.

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

For each creature target player controls, create a token that's a copy of that creature.

Imprint -- When Clone Shell enters the battlefield, look at the top four cards of your library, exile one face down, then put the rest on the bottom of your library in any order.

When Clone Shell dies, turn the exiled card face up. If it's a creature card, put it onto the battlefield under your control.

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

Enchant creature

You control enchanted creature.

Counter target spell.

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.

Whenever an opponent attacks you and/or one or more planeswalkers you control, exile the top card of that player's library. You may play that card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast it.

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

{1}, {T}: Add {U}{B}.

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

{1}{U}{B}: Whenever a card is put into an opponent's graveyard from anywhere this turn, that player loses 1 life.

{2}{U}{B}: Target player mills two cards.

Menace

Whenever Elder Brain attacks a player, exile all cards from that player's hand, then they draw that many cards. You may play lands and cast spells from among the exiled cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.

Deathtouch

When Gonti, Lord of Luxury enters the battlefield, look at the top four cards of target opponent's library, exile one of them face down, then put the rest on the bottom of that library in a random order. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast it.

Gríma, Saruman's Footman can't be blocked.

Whenever Gríma deals combat damage to a player, that player exiles cards from the top of their library until they exile an instant or sorcery card. You may cast that card without paying its mana cost. Then that player puts the exiled cards that weren't cast this way on the bottom of their library in a random order.

Halimar Depths enters tapped.

When Halimar Depths enters, look at the top three cards of your library, then put them back in any order.

{T}: Add {U}.

When Hostage Taker enters, 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.

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

Imprint -- When Isochron Scepter enters, you may exile an instant card with mana value 2 or less from your hand.

{2}, {T}: You may copy the exiled card. If you do, you may cast the copy without paying its mana cost.

+1: Draw a card.

+1: Untap all creatures you control.

-9: Gain control of up to three target creatures.

Flying

When Keiga, the Tide Star dies, gain control of target creature.

Kicker {3}{U}

Each opponent mills eight cards. If this spell was kicked, instead each opponent mills half their library, rounded up.

Gain control of X target creatures and/or planeswalkers.

When Master Thief enters the battlefield, gain control of target artifact for as long as you control Master Thief.

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

Enchant creature

You control enchanted creature.

Dominate Monster -- When Mind Flayer enters the battlefield, gain control of target creature for as long as you control Mind Flayer.

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.

Flying

Whenever Nightveil Specter deals combat damage to a player, that player exiles the top card of their library.

You may play lands and cast spells from among cards exiled with Nightveil Specter.

Once during each of your turns, you may cast a spell from among cards in your graveyard that were milled this turn.

{T}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Exile target nonland card in a graveyard that was put there from anywhere this turn. Copy it. You may cast the copy without paying its mana 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.

Look at the top two cards of target opponent's library. Exile one of them face down and put the other on the bottom of that library. You may look at and play the exiled 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.

Flashback {1}{U}{B}

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

When Solemn Simulacrum enters, 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.

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

({T}: Add {B}.)

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.

{T}: Add {C}{C}. Activate only if you control five or more lands.

+2: Create two 0/1 black Thrull creature tokens.

+1: You may sacrifice another creature or planeswalker. If you do, draw two cards, then draw another card if the sacrificed permanent was a commander.

-10: Gain control of all commanders. Put all commanders from the command zone onto the battlefield under your control.

Tevesh Szat, Doom of Fools can be your commander.

Partner

At the beginning of your end step, if you didn't activate a loyalty ability of a planeswalker this turn, you lose 2 life.

{4}, {T}: For each planeswalker you control, you may activate one of its loyalty abilities once this turn as though none of its loyalty abilities have been activated this turn.

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.

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)

Flying

When Thieving Skydiver enters the battlefield, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to Thieving Skydiver.

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

Islandwalk, swampwalk (This creature can't be blocked as long as defending player controls an Island or a Swamp.)

Whenever Wrexial, the Risen Deep deals combat damage to a player, you may cast target instant or sorcery card from that player's graveyard without paying its mana cost. If that spell would be put into a graveyard, exile it instead.

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.