Re: Fight fight fight!
Marceline really wants to go on the offense and punch some holes into those pirate ships, but stays behind to fight some pirates. She doesn't kill humans, but she does fling those fools far into the ocean and beat the snot out of them. (Anything non-human is fair game for killing unless someone tells her not to. Sorry, non-human pirates. Maybe someone will tell the Marcy Monster to spare you? >>)
If the pirates employ any powered monsters, she's going to prioritize those first.