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.)

Shriekgeist

Flying
Whenever Shriekgeist deals combat damage to a player, that player mills two cards.

Island

Tome Scour

Didn't Say Please

Counter target spell. Its controller mills three cards.

Dream Twist

Target player mills three cards.
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Jace's Phantasm

Flying
Jace's Phantasm gets +4/+4 as long as an opponent has ten or more cards in their graveyard.

Stream of Thought

Target player mills four cards. You shuffle up to four cards from your graveyard into your library.
Replicate {2}{U}{U} (When you cast this spell, copy it for each time you paid its replicate cost. You may choose new targets for the copies.)

Jace's Erasure

Whenever you draw a card, you may have target player mill a card.

Mana Leak

Counter target spell unless its controller pays {3}.

Venture Deeper

Target player mills four cards. (Then exile this card. You may cast the creature later from exile.)

Merfolk Secretkeeper

Merfolk Secretkeeper // Venture Deeper

Frantic Inventory

Draw a card, then draw cards equal to the number of cards named Frantic Inventory in your graveyard.

Thought Scour

Target player mills two cards.
Draw a card.

Sage's Row Denizen

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