Which boss was the most difficult or the coolest?

So far, Dragon Maleficent was the most difficult for me. I had her down to 3 more hits, I was about to die (cure not equipped) she used her green flame and killed me (all without Prince Phillip btw). I fought her again and she started spamming the green flame right off the bat and changed her tactics and I had to use the Prince to defeat her.
My sister is having trouble with Terra's First boss (She is on a higher level though).