Tidal Flats

{U}{U}: For each attacking creature without flying, its controller may pay {1}. If that player doesn't, creatures you control blocking that creature gain first strike until end of turn.

Tidal Influence

Cast this spell only if no permanents named Tidal Influence are on the battlefield.
Tidal Influence enters with a tide counter on it.
At the beginning of your upkeep, put a tide counter on Tidal Influence.
As long as there is exactly one tide counter on Tidal Influence, all blue creatures get -2/-0.
As long as there are exactly three tide counters on Tidal Influence, all blue creatures get +2/+0.
Whenever there are four or more tide counters on Tidal Influence, remove all tide counters from it.

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Deep Spawn

Trample
At the beginning of your upkeep, sacrifice Deep Spawn unless you mill two cards.
{U}: Deep Spawn gains shroud until end of turn and doesn't untap during your next untap step. Tap Deep Spawn. (A creature with shroud can't be the target of spells or abilities.)

Blue Elemental Blast

Choose one —
• Counter target red spell.
• Destroy target red permanent.

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Island

Homarid

Homarid enters with a tide counter on it.
At the beginning of your upkeep, put a tide counter on Homarid.
As long as there is exactly one tide counter on Homarid, it gets -1/-1.
As long as there are exactly three tide counters on Homarid, it gets +1/+1.
Whenever there are four or more tide counters on Homarid, remove all tide counters from it.

Amnesia

Target player reveals their hand and discards all nonland cards.

Braingeyser

Recall

Discard X cards, then return a card from your graveyard to your hand for each card discarded this way. Exile Recall.

Sunken City

At the beginning of your upkeep, sacrifice Sunken City unless you pay {U}{U}.
Blue creatures get +1/+1.

Counterspell

Homarid Spawning Bed

{1}{U}{U}, Sacrifice a blue creature: Create X 1/1 blue Camarid creature tokens, where X is the sacrificed creature's mana value.

Homarid Shaman

Homarid Warrior

{U}: Homarid Warrior gains shroud until end of turn and doesn't untap during your next untap step. Tap Homarid Warrior. (A creature with shroud can't be the target of spells or abilities.)