Consider

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

Izzet Charm

Choose one —
• Counter target noncreature spell unless its controller pays {2}.
• Izzet Charm deals 2 damage to target creature.
• Draw two cards, then discard two cards.

Swamp

Mystical Tutor

Search your library for an instant or sorcery card, reveal it, then shuffle and put that card on top.

Redirect Lightning

As an additional cost to cast this spell, pay 5 life or pay {2}.
Change the target of target spell or ability with a single target.

Thought Vessel

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

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if there are seven or more cards in your graveyard.

Terminate

Destroy target creature. It can't be regenerated.

Command Tower

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

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Zuko, Firebending Master

First strike
Firebending X, where X is the number of experience counters you have. (Whenever this creature attacks, add X {R}. This mana lasts until end of combat.)
Whenever you cast a spell during combat, you get an experience counter.

Ponder

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

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.

Talisman of Dominance

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

Vampiric Tutor

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

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.

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Electrodominance

Electrodominance deals X damage to any target. You may cast a spell with mana value X or less from your hand without paying its mana cost.

Training Center

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

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.

Veyran, Voice of Duality

Magecraft — Whenever you cast or copy an instant or sorcery spell, Veyran gets +1/+1 until end of turn.
If you casting or copying an instant or sorcery spell causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Hexing Squelcher

This spell can't be countered.
Ward—Pay 2 life.
Spells you control can't be countered.
Other creatures you control have "Ward—Pay 2 life."

Fire Lord Azula

Firebending 2 (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
Whenever you cast a spell while Fire Lord Azula is attacking, copy that spell. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.)

Sol Ring

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.

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.

Mountain

Electro, Assaulting Battery

Flying
You don't lose unspent red mana as steps and phases end.
Whenever you cast an instant or sorcery spell, add {R}.
When Electro leaves the battlefield, you may pay {X}. When you do, he deals X damage to target player.

Ral, Leyline Prodigy

Ral enters with an additional loyalty counter on him for each instant and sorcery spell you've cast this turn.
+1: Until your next turn, instant and sorcery spells you cast cost {1} less to cast.
−2: Ral deals 2 damage divided as you choose among one or two targets. Draw a card if you control a blue permanent other than Ral.
−8: Exile the top eight cards of your library. You may cast instant and sorcery spells from among them this turn without paying their mana costs.

Ral, Monsoon Mage

Instant and sorcery spells you cast cost {1} less to cast.
Whenever you cast an instant or sorcery spell during your turn, flip a coin. If you lose the flip, Ral deals 1 damage to you. If you win the flip, you may exile Ral. If you do, return him to the battlefield transformed under his owner's control.

Ral, Monsoon Mage // Ral, Leyline Prodigy

Exotic Orchard

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

Vedalken Orrery

You may cast spells as though they had flash.

Archmage Emeritus

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

Deadly Rollick

If you control a commander, you may cast this spell without paying its mana cost.
Exile target creature.

Haunted Ridge

This land enters tapped unless you control two or more other lands.
{T}: Add {B} or {R}.

Frantic Search

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

Conqueror's Flail

Equipped creature gets +1/+1 for each color among permanents you control.
As long as this Equipment is attached to a creature, your opponents can't cast spells during your turn.
Equip {2}

Nightscape Familiar

Blue spells and red spells you cast cost {1} less to cast.
{1}{B}: Regenerate this creature.

Thrill of Possibility

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

Rakdos Signet

Blood Crypt

({T}: Add {B} or {R}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Dimir Signet

Lier, Disciple of the Drowned

Spells can't be countered.
Each instant and sorcery card in your graveyard has flashback. The flashback cost is equal to that card's mana cost.

Talisman of Indulgence

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

Sulfurous Springs

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

Island

Case of the Ransacked Lab

Instant and sorcery spells you cast cost {1} less to cast.
To solve — You've cast four or more instant and sorcery spells this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Whenever you cast an instant or sorcery spell, draw a card.

Snap

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

Deflecting Swat

If you control a commander, you may cast this spell without paying its mana cost.
You may choose new targets for target spell or ability.

Luxury Suite

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

Invoke Calamity

You may cast up to two instant and/or sorcery spells with total mana value 6 or less from your graveyard and/or hand without paying their mana costs. If those spells would be put into your graveyard, exile them instead. Exile Invoke Calamity.

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.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Sulfur Falls

This land enters tapped unless you control an Island or a Mountain.
{T}: Add {U} or {R}.

Pyretic Ritual

Goblin Electromancer

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

Leyline of Anticipation

If this card is in your opening hand, you may begin the game with it on the battlefield.
You may cast spells as though they had flash.

Borne Upon a Wind

You may cast spells this turn as though they had flash.
Draw a card.

Cloud Key

As this artifact enters, choose artifact, creature, enchantment, instant, or sorcery.
Spells you cast of the chosen type cost {1} less to cast.

Archmage of Runes

Instant and sorcery spells you cast cost {1} less to cast.
Whenever you cast an instant or sorcery spell, draw a card.

Swan Song

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

Morphic Pool

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

Dark Ritual

Abandon Attachments

You may discard a card. If you do, draw two cards.

Dragonskull Summit

This land enters tapped unless you control a Swamp or a Mountain.
{T}: Add {B} or {R}.

Big Score

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.")

Reliquary Tower

Sign in Blood

Target player draws two cards and loses 2 life.

Steam Vents

({T}: Add {U} or {R}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Watery Grave

({T}: Add {U} or {B}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Drowned Catacomb

This land enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Mana Geyser

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

Demonic Tutor

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

Demand Answers

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

Brainstorm

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

High Fae Trickster

Flash (You may cast this spell any time you could cast an instant.)
Flying
You may cast spells as though they had flash.

Firebending Student

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Firebending X, where X is this creature's power. (Whenever this creature attacks, add X {R}. This mana lasts until end of combat.)

Izzet Signet

Seething Song

Thousand-Year Storm

Whenever you cast an instant or sorcery spell, copy it for each other instant and sorcery spell you've cast before it this turn. You may choose new targets for the copies.

Harnfel, Horn of Bounty

Discard a card: Exile the top two cards of your library. You may play those cards this turn.

Birgi, God of Storytelling

Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end.
Creatures you control can boast twice during each of your turns rather than once.

Birgi, God of Storytelling // Harnfel, Horn of Bounty

Stormcatch Mentor

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Instant and sorcery spells you cast cost {1} less to cast.

Inundated Archive

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

Waterlogged Teachings

Search your library for an instant card or a card with flash, reveal it, put it into your hand, then shuffle.

Waterlogged Teachings // Inundated Archive

Ozai, the Phoenix King

Trample, firebending 4, haste
If you would lose unspent mana, that mana becomes red instead.
Ozai has flying and indestructible as long as you have six or more unspent mana.

Underground River

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

Arcane Signet

Talisman of Creativity

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

Bojuka Bog

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