Vanquishing the same baddies can get boring after doing it over and over again. Perhaps it is time to add some variety.
Shield Skeleton. Skeleton holding a piece of shipwreck as a shield. PCs cannot shoot through it, but they can hack it apart with a sword or shoot around it.
Rot Skeleton. It emits a foul miasma around it causing the PC to begin vomiting while near it, maybe even after it is defeated?
Also, make the skeletons without weapons able to pick up dropped kegs and become keg skeletons.
Banshee. Phantom with wild hair that screams (like siren skull) and maybe teleports more than the other ghosts.
Grapple Siren. A siren that grabs onto you and tries to pull you further under the water.
New Melee Weapon: Boarding Axes
Perhaps they hit heavier than a cutlass, but they cannot block as well.
New Improvised Weapon: PC can pick up a snake and throw it at another creature. The snake will attack the one who picks it up if they are holding it long enough, like in a basket, but if it hits another creature, it will hit them.
