Thought Scour

Target player mills two cards.
Draw a card.

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

Dreadwaters

Target player mills X cards, where X is the number of lands you control.

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.)

Drowner Initiate

Whenever a player casts a blue spell, you may pay {1}. If you do, target player mills two cards.

Didn't Say Please

Counter target spell. Its controller mills three cards.

Mind Sculpt

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Winds of Rebuke

Return target nonland permanent to its owner's hand. Each player mills two cards.

Compelling Argument

Target player mills five cards.
Cycling {U} ({U}, Discard this card: Draw a card.)

Counterspell

Island

Sage's Row Denizen

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