CT: Well on my very first play through, Magus's barrier tactic was a real pain in the arse. There wasn't really any boss that could match my parties power. Although I did have problems with that stupid Retinite in the Sunken Dessert and the enemies inside were pretty bad as well. Those Krawlie dudes took off a lot of damage with their tail move. Though many will say Giga Gaia was hard, he wasn't a real threat to me, just maybe sometimes with his triple arm attack moves.
CC: On the first play through, I loved killing that Sun of A Gun boss in Fort Dragonia. Even though it seemed as though my party members took nothing off it physically, I managed to get a HolyLight element from it! Whenever it did that face/mood change, I always laughed because it was hilarious. I'd have to say for the most part, Dario kicked my arse to the moon with Dash&Gash and as well as his ConductaRod whenever I used white elements. What I noticed was if you have Pierre in your party, whenever he attacked him physically and with special moves, Pierre took lesser damage then any of my characters that I had.
Strange . . .