Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Pact of Negation

Counter target spell.
At the beginning of your next upkeep, pay {3}{U}{U}. If you don't, you lose the game.

Leap

Target creature gains flying until end of turn.
Draw a card.

Standstill

When a player casts a spell, sacrifice Standstill. If you do, each of that player's opponents draws three cards.

Time Stretch

Target player takes two extra turns after this one.

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Maze of Ith

{T}: Untap target attacking creature. Prevent all combat damage that would be dealt to and dealt by that creature this turn.

Day's Undoing

Each player shuffles their hand and graveyard into their library, then draws seven cards. If it's your turn, end the turn. (Exile all spells and abilities from the stack, including this card. Discard down to your maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

Helm of Awakening

Beacon of Tomorrows

Target player takes an extra turn after this one. Shuffle Beacon of Tomorrows into its owner's library.

Ghirapur Orrery

Each player may play an additional land on each of their turns.
At the beginning of each player's upkeep, if that player has no cards in hand, that player draws three cards.

Pongify

Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.

Discontinuity

As long as it's your turn, this spell costs {2}{U}{U} less to cast.
End the turn. (Exile all spells and abilities from the stack, including this card. The player whose turn it is discards down to their maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

Wild Evocation

At the beginning of each player's upkeep, that player reveals a card at random from their hand. If it's a land card, the player puts it onto the battlefield. Otherwise, the player casts it without paying its mana cost if able.

Island

Neera, Wild Mage

Whenever you cast a spell, you may put it on the bottom of its owner's library. If you do, reveal cards from the top of your library until you reveal a nonland card. You may cast that card without paying its mana cost. Then put all revealed cards not cast this way on the bottom of your library in a random order. This ability triggers only once each turn.

Chaotic Backlash

Chaotic Backlash deals damage to target player equal to twice the number of white and/or blue permanents they control.

Rapid Hybridization

Destroy target creature. It can't be regenerated. That creature's controller creates a 3/3 green Frog Lizard creature token.

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.

Brainstorm

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

Talisman of Creativity

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

Oath of Mages

At the beginning of each player's upkeep, that player chooses target player who has more life than they do and is their opponent. The first player may have Oath of Mages deal 1 damage to the second player.

Ruby Medallion

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

Drain Power

Target player activates a mana ability of each land they control. Then that player loses all unspent mana and you add the mana lost this way.

Izzet Signet

Vision Skeins

Browbeat

Any player may have Browbeat deal 5 damage to them. If no one does, target player draws three cards.

Ice Cave

Whenever a player casts a spell, any other player may pay that spell's mana cost. If a player does, counter the spell. (Mana cost includes color.)

Fatigue

Target player skips their next draw step.

Vedalken Orrery

You may cast spells as though they had flash.

Arcane Signet

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

Reality Shift

Exile target creature. Its controller manifests the top card of their library. (That player puts the top card of their library onto the battlefield face down as a 2/2 creature. If it's a creature card, it can be turned face up any time for its mana cost.)

Braid of Fire

Cumulative upkeep—Add {R}. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Karn's Temporal Sundering

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Target player takes an extra turn after this one. Return up to one target nonland permanent to its owner's hand. Exile Karn's Temporal Sundering.

Guild Feud

At the beginning of your upkeep, target opponent reveals the top three cards of their library, may put a creature card from among them onto the battlefield, then puts the rest into their graveyard. You do the same with the top three cards of your library. If two creatures are put onto the battlefield this way, those creatures fight each other.

Hurkyl's Final Meditation

As long as it's not your turn, this spell costs {3} more to cast.
Return all nonland permanents to their owners' hands. End the turn. (Exile all spells and abilities from the stack, including this card. The player whose turn it is discards down to their maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

Snap

Return target creature to its owner's hand. Untap up to two lands.

Commander's Sphere

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

Imprisoned in the Moon

Enchant creature, land, or planeswalker
Enchanted permanent is a colorless land with "{T}: Add {C}" and loses all other card types and abilities.

Sapphire Medallion

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

Mana-Charged Dragon

Flying, trample
Join forces — Whenever Mana-Charged Dragon attacks or blocks, each player starting with you may pay any amount of mana. Mana-Charged Dragon gets +X/+0 until end of turn, where X is the total amount of mana paid this way.

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.")

Scroll Rack

{1}, {T}: Exile any number of cards from your hand face down. Put that many cards from the top of your library into your hand. Then look at the exiled cards and put them on top of your library in any order.

Sol Ring

Witness Protection

Enchant creature
Enchanted creature loses all abilities and is a green and white Citizen creature with base power and toughness 1/1 named Legitimate Businessperson. (It loses all other colors, card types, creature types, and names.)

Displacer Kitten

Avoidance — Whenever you cast a noncreature spell, exile up to one target nonland permanent you control, then return that card to the battlefield under its owner's control.

Wash Out

Return all permanents of the color of your choice to their owners' hands.

Tidal Barracuda

Any player may cast spells as though they had flash.
Your opponents can't cast spells during your turn.

Time Warp

Target player takes an extra turn after this one.

Chaotic Transformation

Exile up to one target artifact, up to one target creature, up to one target enchantment, up to one target planeswalker, and/or up to one target land. For each permanent exiled this way, its controller reveals cards from the top of their library until they reveal a card that shares a card type with it, puts that card onto the battlefield, then shuffles.

Time Stop

End the turn. (Exile all spells and abilities from the stack, including this card. The player whose turn it is discards down to their maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

River's Rebuke

Return all nonland permanents target player controls to their owner's hand.

Mana Cache

At the beginning of each player's end step, put a charge counter on Mana Cache for each untapped land that player controls.
Remove a charge counter from Mana Cache: Add {C}. Any player may activate this ability but only during their turn before the end step.

Wild Magic Surge

Destroy target permanent an opponent controls. Its controller reveals cards from the top of their library until they reveal a permanent card that shares a card type with that permanent. They put that card onto the battlefield and the rest on the bottom of their library in a random order.

Time Reversal

Each player shuffles their hand and graveyard into their library, then draws seven cards. Exile Time Reversal.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Rhystic Study

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

Otherworldly Gaze

Surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Explosive Singularity

As an additional cost to cast this spell, you may tap any number of untapped creatures you control. This spell costs {1} less to cast for each creature tapped this way.
Explosive Singularity deals 10 damage to any target.

Crackle with Power

Crackle with Power deals five times X damage to each of up to X targets.

Mountain

Horizon Stone

If you would lose unspent mana, that mana becomes colorless instead.

Moonlace

Target spell or permanent becomes colorless.

Amnesia

Target player reveals their hand and discards all nonland cards.

Narset's Reversal

Copy target instant or sorcery spell, then return it to its owner's hand. You may choose new targets for the copy.

Mind Stone

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

Denying Wind

Search target player's library for up to seven cards and exile them. Then that player shuffles.

Show and Tell

Each player may put an artifact, creature, enchantment, or land card from their hand onto the battlefield.

Redirect

You may choose new targets for target spell.

Thought Vessel

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

Huddle Up

Assist (Another player can pay up to {2} of this spell's cost.)
Two target players each draw a card.