Mark three squares; both players see the water darken. The moment your opponent's next move ends, tentacles erupt from all three at once: any piece standing there except a king is dragged below, and the wreckage blocks those squares for 2 turns.
You draft Leviathan Below in Buff mode. Activated: you choose when to use it, and using it is your move for that turn.
As a attack card, it removes or detonates a piece directly.
“The board is only the surface.”