Consider

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

Mana Leak

Counter target spell unless its controller pays {3}.

Talrand, Sky Summoner

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

Azorius Charm

Choose one —
• Creatures you control gain lifelink until end of turn.
• Draw a card.
• Put target attacking or blocking creature on top of its owner's library.

Monk Class

(Gain the next level as a sorcery to add its ability.)
The second spell you cast each turn costs {1} less to cast.
{W}{U}: Level 2
When this Class becomes level 2, return up to one target nonland permanent to its owner's hand.
{1}{W}{U}: Level 3
At the beginning of your upkeep, exile the top card of your library. For as long as it remains exiled, it has "You may cast this card from exile as long as you've cast another spell this turn."

White Dragon

Flying
Cold Breath — When White Dragon enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Taigam, Ojutai Master

Instant, sorcery, and Dragon spells you control can't be countered.
Whenever you cast an instant or sorcery spell from your hand, if Taigam, Ojutai Master attacked this turn, that spell gains rebound. (Exile the spell as it resolves. At the beginning of your next upkeep, you may cast that card from exile without paying its mana cost.)

Island

Slip Through Space

Devoid (This card has no color.)
Target creature can't be blocked this turn.
Draw a card.

Prowler's Helm

Equipped creature can't be blocked except by Walls.
Equip {2}

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.)

Disenchant

Serum Snare

Return target nonland permanent to its owner's hand. If that permanent had mana value 3 or less, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Anticipate

Look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Shadow Rift

Target creature gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)
Draw a card.

Call to Mind

Return target instant or sorcery card from your graveyard to your hand.

Icingdeath, Frost Tyrant

Flying, vigilance
When Icingdeath, Frost Tyrant dies, create Icingdeath, Frost Tongue, a legendary white Equipment artifact token with "Equipped creature gets +2/+0," "Whenever equipped creature attacks, tap target creature defending player controls," and equip {2}.

Faerie Dragon

Construct

Aven Mindcensor

Flash
Flying
If an opponent would search a library, that player searches the top four cards of that library instead.

Steel of the Godhead

Enchant creature
As long as enchanted creature is white, it gets +1/+1 and has lifelink. (Damage dealt by the creature also causes its controller to gain that much life.)
As long as enchanted creature is blue, it gets +1/+1 and can't be blocked.

Not Forgotten

Put target card from a graveyard on your choice of the top or bottom of its owner's library. Create a 1/1 white Spirit creature token with flying.

Dragonlord Ojutai

Flying
Dragonlord Ojutai has hexproof as long as it's untapped.
Whenever Dragonlord Ojutai deals combat damage to a player, look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Dragon Turtle

Flash
Drag Below — When Dragon Turtle enters, tap it and up to one target creature an opponent controls. They don't untap during their controllers' next untap steps.

Drake

Grand Arbiter Augustin IV

White spells you cast cost {1} less to cast.
Blue spells you cast cost {1} less to cast.
Spells your opponents cast cost {1} more to cast.

Quiet Contemplation

Whenever you cast a noncreature spell, you may pay {1}. If you do, tap target creature an opponent controls and it doesn't untap during its controller's next untap step.

Elminster

Whenever you scry, the next instant or sorcery spell you cast this turn costs {X} less to cast, where X is the number of cards looked at while scrying this way.
+2: Draw a card, then scry 2.
−3: Exile the top card of your library. Create a number of 1/1 blue Faerie Dragon creature tokens with flying equal to that card's mana value.
Elminster can be your commander.

Sejiri Glacier

Sejiri Glacier enters tapped.
{T}: Add {W}.

Sejiri Shelter

Target creature you control gains protection from the color of your choice until end of turn.

Sejiri Shelter // Sejiri Glacier

Haughty Djinn

Flying
Haughty Djinn's power is equal to the number of instant and sorcery cards in your graveyard.
Instant and sorcery spells you cast cost {1} less to cast.

Loran's Escape

Target artifact or creature gains hexproof and indestructible until end of turn. Scry 1.

Kairi, the Swirling Sky

Flying, ward {3}
When Kairi, the Swirling Sky dies, choose one —
• Return any number of target nonland permanents with total mana value 6 or less to their owners' hands.
• Mill six cards, then return up to two instant and/or sorcery cards from your graveyard to your hand.

Counterspell

Iymrith, Desert Doom

Flying
Iymrith, Desert Doom has ward {4} as long as it's untapped.
Whenever Iymrith deals combat damage to a player, draw a card. Then if you have fewer than three cards in hand, draw cards equal to the difference.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Oji, the Exquisite Blade

When Oji, the Exquisite Blade enters, you gain 2 life and scry 2.
Whenever you cast your second spell each turn, exile up to one target creature you control, then return it to the battlefield under its owner's control.

Impulse

Look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Jace's Sanctum

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

Soulherder

Whenever a creature is exiled from the battlefield, put a +1/+1 counter on Soulherder.
At the beginning of your end step, you may exile another target creature you control, then return that card to the battlefield under its owner's control.

Mystic Sanctuary

({T}: Add {U}.)
Mystic Sanctuary enters tapped unless you control three or more other Islands.
When Mystic Sanctuary enters untapped, you may put target instant or sorcery card from your graveyard on top of your library.

Dispel

Boon of Safety

Put a shield counter on target creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Scry 1.

Vega, the Watcher

Flying
Whenever you cast a spell from anywhere other than your hand, draw a card.

Kayla's Command

Choose two —
• Create a 2/2 colorless Construct artifact creature token.
• Put a +1/+1 counter on a creature you control. It gains double strike until end of turn.
• Search your library for a basic Plains card, reveal it, put it into your hand, then shuffle.
• You gain 2 life and scry 2.

Azorius Chancery

Azorius Chancery enters tapped.
When Azorius Chancery enters, return a land you control to its owner's hand.
{T}: Add {W}{U}.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Shelter

Target creature you control gains protection from the color of your choice until end of turn.
Draw a card.

Winged Boots

Equipped creature has flying and ward {4}. (Whenever equipped creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {4}.)
Equip {1}

Capsizing Wave

Return target creature to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Sword Coast Serpent

Sword Coast Serpent can't be blocked as long as you've cast a noncreature spell this turn.

Sword Coast Serpent // Capsizing Wave

Wrath of God

Destroy all creatures. They can't be regenerated.

Cloudshift

Exile target creature you control, then return that card to the battlefield under your control.

Sunscorch Regent

Flying
Whenever an opponent casts a spell, put a +1/+1 counter on Sunscorch Regent and you gain 1 life.

Pristine Skywise

Flying
Whenever you cast a noncreature spell, untap Pristine Skywise. It gains protection from the color of your choice until end of turn.

Plains

Icingdeath, Frost Tongue

Equipped creature gets +2/+0.
Whenever equipped creature attacks, tap target creature defending player controls.
Equip {2}

See the Truth

Look at the top three cards of your library. Put one of those cards into your hand and the rest on the bottom of your library in any order. If this spell was cast from anywhere other than your hand, put each of those cards into your hand instead.

Cursed Totem

Activated abilities of creatures can't be activated.

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters tapped unless you control two or more basic lands.

Dragon's Disciple

As Dragon's Disciple enters, you may reveal a Dragon card from your hand. If you do or if you control a Dragon, Dragon's Disciple enters with a +1/+1 counter on it.
Dragons you control have ward {1}. (Whenever a Dragon you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

Juvenile Mist Dragon

Flying
Confounding Clouds — When Juvenile Mist Dragon enters, for each opponent, tap up to one target creature that player controls. Each of those creatures doesn't untap during its controller's next untap step.

Port Town

As Port Town enters, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters tapped.
{T}: Add {W} or {U}.

Swarm Intelligence

Whenever you cast an instant or sorcery spell, you may copy that spell. You may choose new targets for the copy.

Negate

Containment Priest

Flash
If a nontoken creature would enter and it wasn't cast, exile it instead.

Mercurial Spelldancer

Mercurial Spelldancer can't be blocked.
Whenever you cast a noncreature spell, put an oil counter on Mercurial Spelldancer.
Whenever Mercurial Spelldancer deals combat damage to a player, you may remove two oil counters from it. If you do, when you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

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.

Relearn

Triskaidekaphile

You have no maximum hand size.
At the beginning of your upkeep, if you have exactly thirteen cards in your hand, you win the game.
{3}{U}: Draw a card.

Spirit

Stenn, Paranoid Partisan

As Stenn, Paranoid Partisan enters, choose a card type other than creature or land.
Spells you cast of the chosen type cost {1} less to cast.
{1}{W}{U}: Exile Stenn. Return it to the battlefield under its owner's control at the beginning of the next end step.

Yosei, the Morning Star

Flying
When Yosei, the Morning Star dies, target player skips their next untap step. Tap up to five target permanents that player controls.

Warden of Evos Isle

Flying
Creature spells with flying you cast cost {1} less to cast.

Watcher of the Spheres

Flying
Creature spells with flying you cast cost {1} less to cast.
Whenever another creature you control with flying enters, Watcher of the Spheres gets +1/+1 until end of turn.

Chart a Course

Draw two cards. Then discard a card unless you attacked this turn.

Ghostly Prison

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Blue Dragon

Flying
Lightning Breath — When Blue Dragon enters, until your next turn, target creature an opponent controls gets -3/-0, up to one other target creature gets -2/-0, and up to one other target creature gets -1/-0.

Portent

Look at the top three cards of target player's library, then put them back in any order. You may have that player shuffle.
Draw a card at the beginning of the next turn's upkeep.