Black Lotus

{T}, Sacrifice Black Lotus: Add three mana of any one color.

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Merfolk of the Pearl Trident

Counterspell

Time Walk

Tropical Island

Mox Emerald

Mox Sapphire

Mana Short

Tap all lands target player controls and that player loses all unspent mana.

Braingeyser

Prevent all combat damage that would be dealt this turn.

Channel

Until end of turn, any time you could activate a mana ability, you may pay 1 life. If you do, add {C}.

Giant Growth

Target creature gets +3/+3 until end of turn.

Black Vise

As Black Vise enters, choose an opponent.
At the beginning of the chosen player's upkeep, Black Vise deals X damage to that player, where X is the number of cards in their hand minus 4.