Viscerid Drone

{T}, Sacrifice a creature and a Swamp: Destroy target nonartifact creature. It can't be regenerated.
{T}, Sacrifice a creature and a snow Swamp: Destroy target creature. It can't be regenerated.

Homarid Shaman

Spiny Starfish

{U}: Regenerate Spiny Starfish.
At the beginning of each end step, if Spiny Starfish regenerated this turn, create a 0/1 blue Starfish creature token for each time it regenerated this 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.

Coral Reef

Coral Reef enters with four polyp counters on it.
Sacrifice an Island: Put two polyp counters on Coral Reef.
{U}, Tap an untapped blue creature you control, Remove a polyp counter from Coral Reef: Put a +0/+1 counter on target creature.

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.