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.

Mishra's Bauble

{T}, Sacrifice Mishra's Bauble: Look at the top card of target player's library. Draw a card at the beginning of the next turn's upkeep.

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.

Aether Vial

At the beginning of your upkeep, you may put a charge counter on ?ther Vial. {T}: You may put a creature card with converted mana cost equal to the number of charge counters on ?ther Vial from your hand onto the battlefield.

Spellskite

{U/P}: Change a target of target spell or ability to Spellskite. ({U/P} can be paid with either {U} or 2 life.)

Mutavault

{T}: Add {1} to your mana pool. {1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Darkslick Shores

Darkslick Shores enters the battlefield tapped unless you control two or fewer other lands. {T}: Add {U} or {B} to your mana pool.

Cursecatcher

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

Thoughtseize

Target player reveals his or her hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Lord of Atlantis

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

Unearth

Cycling {2} (You may pay {2} and discard this card from your hand to draw a card. Play this ability as an instant.) Choose target creature card in your graveyard with total casting cost 3 or less and put that creature into play.

Spreading Seas

Enchant land When Spreading Seas enters the battlefield, draw a card. Enchanted land is an Island.

Polluted Delta

Scalding Tarn

Watery Grave

Fatal Push

Hope of Ghirapur

Damping Sphere

If a land is tapped for two or more mana, it produces {C} instead of any other type and amount. Each spell a player casts costs {1} more to cast for each other spell that player has cast this turn.

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.

Mystical Dispute

This spell costs {2} less to cast if it targets a blue spell. Counter target spell unless its controller pays {3}.

Lurrus of the Dream-Den

Companion — Each permanent card in your starting deck has converted mana cost 2 or less. (If this card is your chosen companion, you may cast it once from outside the game.) Lifelink During each of your turns, you may cast one permanent spell with converted mana cost 2 or less from your graveyard.

Island

({T}: Add {U}.)