Consider

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

Reliquary Tower

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

Polymorphist's Jest

Until end of turn, each creature target player controls loses all abilities and becomes a blue Frog with base power and toughness 1/1.

Propaganda

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

Aetherize

Return all attacking creatures to their owner's hand.

Complicate

Counter target spell unless its controller pays {3}.
Cycling {2}{U} ({2}{U}, Discard this card: Draw a card.)
When you cycle Complicate, you may counter target spell unless its controller pays {1}.

Deduce

Draw a card. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Whirlwind Denial

For each spell and ability your opponents control, counter it unless its controller pays {4}.

Galestrike

Return target tapped creature to its owner's hand.
Draw a card.

Island

Mana Leak

Counter target spell unless its controller pays {3}.

Geyser Drake

Flying
During turns other than yours, spells you cast cost {1} less to cast.

Baral, Chief of Compliance

Instant and sorcery spells you cast cost {1} less to cast.
Whenever a spell or ability you control counters a spell, you may draw a card. If you do, discard a card.

Heraldic Banner

As this artifact enters, choose a color.
Creatures you control of the chosen color get +1/+0.
{T}: Add one mana of the chosen color.

Palladium Myr

Sky Diamond

Archaeomancer

When Archaeomancer enters, return target instant or sorcery card from your graveyard to your hand.

Deprive

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

Essence Capture

Counter target creature spell. Put a +1/+1 counter on up to one target creature you control.

Personal Tutor

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

Neutralizing Blast

Bone to Ash

Counter target creature spell.
Draw a card.

Coastal Piracy

Whenever a creature you control deals combat damage to an opponent, you may draw a card.

Cancel

Exclude

Repulse

Return target creature to its owner's hand.
Draw a card.

Scourge of Fleets

When Scourge of Fleets enters, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.

Talrand, Sky Summoner

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

Quench

Counter target spell unless its controller pays {2}.

Opposition

Tap an untapped creature you control: Tap target artifact, creature, or land.

Visions of Beyond

Draw a card. If a graveyard has twenty or more cards in it, draw three cards instead.

Mind Stone

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

Sapphire Medallion

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

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Sol Ring

Remove Soul

Extraplanar Lens

Imprint — When Extraplanar Lens enters, you may exile target land you control.
Whenever a land with the same name as the exiled card is tapped for mana, its controller adds one mana of any type that land produced.

Spell Syphon

Counter target spell unless its controller pays {1} for each blue permanent you control.

Refute

Counter target spell. Draw a card, then discard a card.

Disrupt

Counter target instant or sorcery spell unless its controller pays {1}.
Draw a card.

Mystical Tutor

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

Abjure

As an additional cost to cast this spell, sacrifice a blue permanent.
Counter target spell.

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Archmage Emeritus

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

Murmuring Mystic

Whenever you cast an instant or sorcery spell, create a 1/1 blue Bird Illusion creature token with flying.

Military Intelligence

Whenever you attack with two or more creatures, draw a card.

Teferi's Ageless Insight

If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

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.)

Wavebreak Hippocamp

Whenever you cast your first spell during each opponent's turn, draw a card.

Disallow

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

Neutralize

Counter target spell.
Cycling {2} ({2}, Discard this card: Draw a card.)

Castle Vantress

Castle Vantress enters tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 2.

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.

Deliberate

Flood of Recollection

Return target instant or sorcery card from your graveyard to your hand. Exile Flood of Recollection.

Into the Roil

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, draw a card.

Think Twice

Draw a card.
Flashback {2}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Dispel

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

Unwind

Counter target noncreature spell. Untap up to three lands.

Rakshasa's Disdain

Counter target spell unless its controller pays {1} for each card in your graveyard.

Meeting of Minds

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.)
Draw two cards.

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.")

Traveler's Amulet

{1}, Sacrifice Traveler's Amulet: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.