I would clarify what this means – can shoot at submerged ships, can ram them, etc
It would function similar to the abilities of Cadara and Shaihulud, without the submarine restriction. Hopefully the following clears it up.
Leviathan
A game piece with this keyword is a Sea Creature.
Leviathans have 7 segments (six claws, one head); however Leviathans may not always have cannons assigned to all their segments. Only segments with cannons shown can shoot. A leviathan’s segments cannot be eliminated unless the cannon roll is a 6. After a leviathan resolves a move action, as a free action it may repair any one missing segment.
At the beginning of your turn decide if a Leviathan is submerged or on the surface.
If submerged a leviathan may be given move actions, it cannot touch other ships and cannot be shot at. While submerged a leviathan may be given shoot actions to target submerged ships. While submerged, as part of a move action a leviathan may initiate a boarding party against an enemy ship up to S away without ramming.
If on the surface a leviathan may move and be given shoot actions (it may target submerged ships); it may ram opposing ships (the rammed ship becomes pinned instead) and it may board. After winning a boarding party the leviathan may eliminate a crew or steal a treasure (if cargo space permits), but it cannot capture crew and if it takes a unique treasure that treasure is eliminated.
When a Leviathan is given a shoot action,you may choose whether that action is a normal shoot action or a lightning attack (it cannot perform both with a single action). A lightning attack can be initiated even if the Leviathan is submerged, and allows a Leviathan a rank-2 attack against any one target (including submerged ships) within L+L of its head. If the attack hits, eliminate up to two masts from the target ship, as well as any other ship in the line of fire with the attack.