The doom dragon was easy.
Of course, if you transfer your data from the first Golden Sun then you get more Djinni if you got them all in that game.
I always found Star magician to be the hardest, because he always like to have his balls blow up in my face and kill me
Edit: also, how do you die if you mess up one turn? if your party is all wiped out, the reserve party comes to the front.