Ansem gave the most sage advice, or at least the closest to what I used that worked. Just pay attention to the cauldron, keep moving, and blast the cauldron with the opposing element to it's color (I don't think I've ever seen it go yellow, though....). Soon as Ursala is dazed, GO FREAKIN' BALLISTIC. She has pathetic defence, so in a round, you should be able to almost defeat her. I did it in two stuns (admittedly, VERY spaced apart....) Anyone done better?

Oh, and to build up some hope for you...you think THIS is bad? it's just a warm-up for the nightmare to come...