Venture Deeper

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

Merfolk Secretkeeper

Counter target spell. Its controller mills three cards.

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

Constellation — Whenever Thassa's Devourer or another enchantment you control enters, target player mills two cards.

Target player mills two cards.
Draw a card.

Enchant player
At the beginning of enchanted player's upkeep, that player mills two cards.

Return target creature to its owner's hand. Untap up to two lands.

Draw three cards, then put two cards from your hand on top of your library in any order.