First! Make sure yuor party (which should consists of Sora,Donald,& Jack) is at Lv. 26-30 to make this battle easier. When the fight starts, find and kill the lizard heartless to bring back the light(do this everytime it get pitch black) then find Barbosa.If you have Donald in you party he will use magic on him (his weakness) really all there is to do if your prepard is beat the shit out of him.
if this doesnt help,tell me and ill give a more detailed strategy.