Starlit Mantle

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature you control
When this Aura enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Wall of Lost Thoughts

Defender (This creature can't attack.)
When this creature enters, target player mills four cards. (They put the top four cards of their library into their graveyard.)

Weight of Memory

Draw three cards. Target player mills three cards.

Storm Sculptor

This creature can't be blocked.
When this creature enters, return a creature you control to its owner's hand.

Merfolk Sovereign

Other Merfolk creatures you control get +1/+1.
{T}: Target Merfolk creature can't be blocked this turn.

Towering-Wave Mystic

Whenever this creature deals damage, target player mills that many cards.

Island

Winds of Rebuke

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

Thriving Isle

This land enters tapped. As it enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

Shaper Apprentice

This creature has flying as long as you control another Merfolk.

River Sneak

This creature can't be blocked.
Whenever another Merfolk you control enters, this creature gets +1/+1 until end of turn.

Watertrap Weaver

When this creature enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Compelling Argument

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

Venture Deeper

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