Force of Will

You may pay 1 life and remove a blue card in your hand from the game instead of paying Force of Will's casting cost. Effects that prevent or redirect damage cannot be used to counter this loss of life. Counter target spell.

Cavern of Souls

As Cavern of Souls enters the battlefield, choose a creature type. {T}: Add {1} to your mana pool. {T}: Add one mana of any color to your mana pool. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.

True-Name Nemesis

As True-Name Nemesis enters the battlefield, choose a player. True-Name Nemesis has protection from the chosen player. (This creature can't be blocked, targeted, dealt damage, or enchanted by anything controlled by that player.)

Phantasmal Image

You may have Phantasmal Image enter the battlefield as a copy of any creature on the battlefield, except it's an Illusion in addition to its other types and it gains "When this creature becomes the target of a spell or ability, sacrifice it."

Master of the Pearl Trident

Other Merfolk creatures you control get +1/+1 and have islandwalk. (They are unblockable as long as defending player controls an Island.)

Harbinger of the Tides

You may cast Harbinger of the Tides as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.) When Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

Daze

You may return an island you control to its owner's hand instead of paying Daze's mana cost. Counter target spell unless its controller pays {1}.

Mental Misstep

({U/P} can be paid with either {U} or 2 life.) Counter target spell with converted mana cost 1.

Vapor Snag

Return target creature to its owner's hand. Its controller loses 1 life.

Merrow Reejerey

Other Merfolk creatures you control get +1/+1. Whenever you play a Merfolk spell, you may tap or untap target permanent.

Cursecatcher

Sacrifice Cursecatcher: Counter target instant or sorcery spell unless its controller pays {1}.

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Remove target player's graveyard from the game.

Mox Sapphire

Add 1 blue mana to your mana pool. Tapping this artifact can be played as an interrupt.

Lord of Atlantis

All Merfolk in play gain islandwalk and +1/+1 while this card is in play.

Time Walk

Take an extra turn after this one.

Ancestral Recall

Draw 3 cards or force opponent to draw 3 cards.

Black Lotus

Adds 3 mana of any single color of your choice to your mana pool, then is discarded. Tapping this artifact can be played as an interrupt.

Null Rod

Players cannot play any artifact abilities requiring an activation cost.

Strip Mine

Silvergill Adept

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}. When Silvergill Adept enters the battlefield, draw a card.