Negate

Fleeting Memories

When Fleeting Memories enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
Whenever you sacrifice a Clue, target player mills three cards.

Floodhound

{3}, {T}: Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Tamiyo's Epiphany

Zulaport Duelist

Flash
When Zulaport Duelist enters, up to one target creature gets -2/-0 until end of turn. Its controller mills two cards. (They put the top two cards of their library into their graveyard.)

Mindstatic

Counter target spell unless its controller pays {6}.

Scuttletide

{1}, Discard a card: Create a 0/3 blue Crab creature token.
Delirium — Crabs you control get +1/+1 as long as there are four or more card types among cards in your graveyard.

Dispel

Lay Bare

Counter target spell. Look at its controller's hand.

Passwall Adept

{2}{U}: Target creature can't be blocked this turn.

Annul

Counter target artifact or enchantment spell.

Cancel

Tazeem Roilmage

Kicker {4} (You may pay an additional {4} as you cast this spell.)
When Tazeem Roilmage enters, if it was kicked, return target instant or sorcery card from your graveyard to your hand.

Second Guess

Counter target spell that's the second spell cast this turn.

Moonblade Shinobi

Ninjutsu {2}{U} ({2}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Moonblade Shinobi deals combat damage to a player, create a 1/1 blue Illusion creature token with flying.

Mulldrifter

Flying
When Mulldrifter enters, draw two cards.
Evoke {2}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Spell Snuff

Counter target spell.
Fateful hour — If you have 5 or less life, draw a card.

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Behold the Multiverse

Scry 2, then draw two cards.
Foretell {1}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Essence Scatter

Nullify

Skaab Wrangler

Tap three untapped creatures you control: Tap target creature.

Thunder Drake

Flying
Whenever you cast your second spell each turn, put a +1/+1 counter on Thunder Drake.

Tightening Coils

Enchant creature
Enchanted creature gets -6/-0 and loses flying.

Shared Discovery

As an additional cost to cast this spell, tap four untapped creatures you control.
Draw three cards.

Read the Tides

Choose one —
• Draw three cards.
• Return up to two target creatures to their owners' hands.

Cloudkin Seer

Flying
When Cloudkin Seer enters, draw a card.

Island

Mental Journey

Draw three cards.
Basic landcycling {1}{U} ({1}{U}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

Scribe of the Mindful

{1}, {T}, Sacrifice Scribe of the Mindful: Return target instant or sorcery card from your graveyard to your hand.

Outwit

Counter target spell that targets a player.

Sage's Row Denizen

Whenever another blue creature you control enters, target player mills two cards.