Wow, I guess I'm like, the ultimate loser when it comes to the boss fights with the Organization members. XD I die a million times on them (Except Luxord.).
Quite honestly, all of them gave me a pretty hard time (Except Luxord.), although for Saix, it was mostly my fault on my timing and stuff.
The last form for Xemnas and the weird airship thing were probably hardest. For the airship thing, I didn't use laser at first because I thought it would deplete my energy bar, but I decided to give it a go after dying for the fiftieth time. Turns out it's a lot more effective than the megabeam.
And the final boss, the only parts that killed me were when I controlled Riku (Goddamn shields kill me. But spamming dark aura works well.) and the laser room of doom (but only because I didn't realize I had to push X AND triangle button. :O). I would get mad at Sora, because he's standing there like an idiot while Riku's doing all those crazy reflecting.
Aside from him, Xigbar killed me lots when he got all trigger happy on that little platform. I don't even die from that attack, I get killed afterwards when I'm almost dead and the stupid guy shoots me before I can heal. What pissed me off even more was that Donald and Goofy usually end up unscathed from those attacks. But then I learned that running around like a mad person on the platform pretty much dodges all the bullets, so yay.
I probably wrote more than anyone will bother to read, but oh well.