Swamp

Brinelin, the Moon Kraken

When Brinelin, the Moon Kraken enters and whenever you cast a spell with mana value 6 or greater, you may return target nonland permanent to its owner's hand.
Partner (You can have two commanders if both have partner.)

Tightening Coils

Enchant creature
Enchanted creature gets -6/-0 and loses flying.

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Unknown Shores

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Take Inventory

Draw a card, then draw cards equal to the number of cards named Take Inventory in your graveyard.

Drag Under

Return target creature to its owner's hand.
Draw a card.

Island

Kraken Hatchling

Quest for Ula's Temple

At the beginning of your upkeep, you may look at the top card of your library. If it's a creature card, you may reveal it and put a quest counter on Quest for Ula's Temple.
At the beginning of each end step, if there are three or more quest counters on Quest for Ula's Temple, you may put a Kraken, Leviathan, Octopus, or Serpent creature card from your hand onto the battlefield.

Submerged Boneyard

Submerged Boneyard enters tapped.
{T}: Add {U} or {B}.

High Tide

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

Scourge of Fleets

When Scourge of Fleets enters, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.