Tbh i had so much fun chaining monsters, rare game hunting and treasure hunting that most of the time i was somewhat over levelled for the story bosses and such i didn't really struggle with any of them.

Marks though... I remember being killed by a cactuars 1000 needles when i decided to fight him with a party of just vaan. The Wyrm in the paramina rift gave me a spot of trouble too. I think it goes without saying that Zodiark put up a good fight. He never actually killed my party, i managed to hang in there but ive never had such an intense fight. Not even Yiazmat put up as much of a fight as him