No worries! It took me a week when I was on Standard (I didn't know how to use limits!) Just use your limits and reaction commands, and get as many hi-potions as you can get. And equip as many limits with Donald and Goofy and becareful if Demyx brings you into the Show Stealer move, he can really inflict a lot of damage on you. And when he says come on kick to the beat, just jump away from him (if you have already leveled up you valor form then go equip it). Try cornnering him but there are high changes he may just run and put geysers all over you. And when he starts lineing those bubbles up and shoots them at you jump with the high jump, cuz chances are he'll get you if you don't have that. I think that'll help ya.