The ocean at Mal Pais, can be dangerous when the waves get big, especially during summer.
SO be carefull when swimming, and at days it is better to just swim in the hotel pool, cause there are no lifeguards on duty here.
Well you are in the tropics, and there is malaria present. I didn't take any medication for it, but that was my own choice, I just tried to avoid the little buggers, and I succeeded.
But reppellent is a good thing to bring, even though the mozzies here aren't as bad as in other parts in Central America.