This is assuming “its submerged status” is in regards to the Leviathan, because if it’s in reference to any enemy submerged ship, that part is already covered by the part in parentheses.
I may need to revise the wording again. A submerged Leviathan can shoot normally at any submerged ship (submarine, Sea Monster, etc), but while submerged a leviathan cannot use its regular cannons against a ship on the surface. The lightning attack can be used by a Leviathan while it is submerged or on the surface, and can target any enemy ship that is submerged or on the surface. For example, a surfaced Leviathan could target a submerged Sea Monster with the lightning attack, or a submerged leviathan could target a submerged submarine with the lightning attack.
I assume the “it may board” refers to the Leviathan? One could argue that is in reference to the rammed ship instead.
Yes, it refers to the Leviathan being able to board the pinned ship.
Does 30 points for the example leviathan feel fair or still too cheap for what the keyword can do as-is?