Consider

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

Pongify

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

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Rakdos Signet

Arcane Signet

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

Baral and Kari Zev

First strike, menace
Whenever you cast your first instant or sorcery spell each turn, you may cast a spell with lesser mana value that shares a card type with it from your hand without paying its mana cost. If you don't, create First Mate Ragavan, a legendary 2/1 red Monkey Pirate creature token. It gains haste until end of turn.

Archmage Emeritus

Magecraft — Whenever you cast or copy an instant or sorcery spell, draw a card.

Vraska's Fall

Each opponent sacrifices a creature or planeswalker of their choice and gets a poison counter.

Anhelo, the Painter

Deathtouch
The first instant or sorcery spell you cast each turn has casualty 2. (As you cast that spell, you may sacrifice a creature with power 2 or greater. When you do, copy the spell and you may choose new targets for the copy.)

Mizzix's Mastery

Exile target card that's an instant or sorcery from your graveyard. For each card exiled this way, copy it, and you may cast the copy without paying its mana cost. Exile Mizzix's Mastery.
Overload {5}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Mana Geyser

Add {R} for each tapped land your opponents control.

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Reliquary Tower

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

Bojuka Bog

This land enters tapped.
When this land enters, exile target player's graveyard.
{T}: Add {B}.

Deadly Dispute

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw two cards and create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Audacious Swap

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell and you may choose a new target for the copy.)
The owner of target nonenchantment permanent shuffles it into their library, then exiles the top card of their library. If it's a land card, they put it onto the battlefield. Otherwise, they may cast it without paying its mana cost.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Snap

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

Demonic Tutor

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

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. This artifact deals 1 damage to you.

Cabal Coffers

{2}, {T}: Add {B} for each Swamp you control.

Sol Ring

Fact or Fiction

Reveal the top five cards of your library. An opponent separates those cards into two piles. Put one pile into your hand and the other into your graveyard.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Exotic Orchard

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

Cruel Ultimatum

Target opponent sacrifices a creature of their choice, discards three cards, then loses 5 life. You return a creature card from your graveyard to your hand, draw three cards, then gain 5 life.

Thought Vessel

Expropriate

Council's dilemma — Starting with you, each player votes for time or money. For each time vote, take an extra turn after this one. For each money vote, choose a permanent owned by the voter and gain control of it. Exile Expropriate.

Command Tower

Storm-Kiln Artist

This creature gets +1/+0 for each artifact you control.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a Treasure token.

Jeska's Will

Choose one. If you control a commander as you cast this spell, you may choose both instead.
• Add {R} for each card in target opponent's hand.
• Exile the top three cards of your library. You may play them this turn.

Display of Power

This spell can't be copied.
Copy any number of target instant and/or sorcery spells. You may choose new targets for the copies.

Dimir Signet

Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Bedevil

Destroy target artifact, creature, or planeswalker.

Brass's Bounty

For each land you control, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Reverberate

Copy target instant or sorcery spell. You may choose new targets for the copy.

Ancient Tomb

{T}: Add {C}{C}. This land deals 2 damage to you.

Aetherflux Reservoir

Whenever you cast a spell, you gain 1 life for each spell you've cast this turn.
Pay 50 life: This artifact deals 50 damage to any target.

Twincast

Training Center

This land enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

Time Warp

Target player takes an extra turn after this one.

Talisman of Indulgence

{T}: Add {C}.
{T}: Add {B} or {R}. This artifact deals 1 damage to you.

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Fellwar Stone

Poppet Factory

Creature tokens you control lose all abilities and have base power and toughness 3/3.
At the beginning of your upkeep, you may transform Poppet Factory.

Poppet Stitcher

Whenever you cast an instant or sorcery spell, create a 2/2 black Zombie creature token with decayed. (It can't block. When it attacks, sacrifice it at end of combat.)
At the beginning of your upkeep, if you control three or more creature tokens, you may transform Poppet Stitcher.

Poppet Stitcher // Poppet Factory

Complete the Circuit

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
You may cast sorcery spells this turn as though they had flash.
When you next cast an instant or sorcery spell this turn, copy that spell twice. You may choose new targets for the copies.

Takenuma, Abandoned Mire

{T}: Add {B}.
Channel — {3}{B}, Discard this card: Mill three cards, then return a creature or planeswalker card from your graveyard to your hand. This ability costs {1} less to activate for each legendary creature you control.

Cryptic Pursuit

Whenever you cast an instant or sorcery spell from your hand, manifest the top card of your library. (Put that card onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
Whenever a face-down creature you control dies, exile it if it's an instant or sorcery card. You may cast that card until the end of your next turn.

Sorcerer Class

(Gain the next level as a sorcery to add its ability.)
When Sorcerer Class enters, draw two cards, then discard two cards.
{U}{R}: Level 2
Creatures you control have "{T}: Add {U} or {R}. Spend this mana only to cast an instant or sorcery spell or to gain a Class level."
{3}{U}{R}: Level 3
Whenever you cast an instant or sorcery spell, that spell deals damage to each opponent equal to the number of instant and sorcery spells you've cast this turn.

Jadar, Ghoulcaller of Nephalia

At the beginning of your end step, if you control no creatures with decayed, create a 2/2 black Zombie creature token with decayed. (It can't block. When it attacks, sacrifice it at end of combat.)

Storm King's Thunder

When you next cast an instant or sorcery spell this turn, copy that spell X times. You may choose new targets for the copies.

Otawara, Soaring City

{T}: Add {U}.
Channel — {3}{U}, Discard this card: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

Cormela, Glamour Thief

Haste
{1}, {T}: Add {U}{B}{R}. Spend this mana only to cast instant and/or sorcery spells.
When Cormela dies, return up to one target instant or sorcery card from your graveyard to your hand.

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Seething Song

Morphic Pool

This land enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Dockside Extortionist

When this creature enters, create X Treasure tokens, where X is the number of artifacts and enchantments your opponents control. (Treasure tokens are artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Errant, Street Artist

Flash
Defender, haste
{1}{U}, {T}: Copy target spell you control that wasn't cast. You may choose new targets for the copy.

Make an Example

Each opponent separates the creatures they control into two piles. For each opponent, you choose one of their piles. Each opponent sacrifices the creatures in their chosen pile. (Piles can be empty.)

Reiterate

Buyback {3} (You may pay an additional {3} as you cast this spell. If you do, put this card into your hand as it resolves.)
Copy target instant or sorcery spell. You may choose new targets for the copy.

Luxury Suite

This land enters tapped unless you have two or more opponents.
{T}: Add {B} or {R}.

Murkwater Pathway

Clearwater Pathway

Clearwater Pathway // Murkwater Pathway

Lavaglide Pathway

Riverglide Pathway

Riverglide Pathway // Lavaglide Pathway

Jaya's Immolating Inferno

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Jaya's Immolating Inferno deals X damage to each of up to three targets.

Twinning Staff

If you would copy a spell one or more times, instead copy it that many times plus an additional time. You may choose new targets for the additional copy.
{7}, {T}: Copy target instant or sorcery spell you control. You may choose new targets for the copy.

Fury Storm

When you cast this spell, copy it for each time you've cast your commander from the command zone this game. You may choose new targets for the copies.
Copy target instant or sorcery spell. You may choose new targets for the copy.

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.

Torment of Hailfire

Repeat the following process X times. Each opponent loses 3 life unless that player sacrifices a nonland permanent of their choice or discards a card.

Cascade Bluffs

{T}: Add {C}.
{U/R}, {T}: Add {U}{U}, {U}{R}, or {R}{R}.

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. This artifact deals 1 damage to you.

Wizards of Thay

Myriad (Whenever this creature attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)
Instant and sorcery spells you cast cost {1} less to cast.
You may cast sorcery spells as though they had flash.

Brainstorm

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

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Snow-Covered Mountain

Talrand, Sky Summoner

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

Goblin Electromancer

Instant and sorcery spells you cast cost {1} less to cast.

Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

Field of the Dead

This land enters tapped.
{T}: Add {C}.
Whenever this land or another land you control enters, if you control seven or more lands with different names, create a 2/2 black Zombie creature token.

Searstep Pathway

Blightstep Pathway

Blightstep Pathway // Searstep Pathway

Worst Fears

You control target player during that player's next turn. Exile Worst Fears. (You see all cards that player could see and make all decisions for the player.)

Unexpected Windfall

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Snow-Covered Island

Comet Storm

Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.)
Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.