Awesome ideas Elrade! Though make sure that the characters are tough enough to fight, and that Limits should be available too, but overall, excellent ideas!
However, as for Golden Mountains, Yzma doesn't really look like the fighting type, but maybe should could use non-Physical attacks if you know what I mean
She'd get Kronk and the royal guard to do the fighting, or she could throw potions. And when she changes into a cat, she could jsut scratch you up!
She'd be the easiest and funniest boss in the game, especially because your esperience level would be higher.