For me it was the Dragonrider. Once I found out you should fight him without lock-on, I could just run around him all the time and attack him with ease. --- Always know your endgame before you lift a hand.
Last Giant... Don't get me wrong, Dragon Rider is a pushover... But Last Giant has the same problem as most giant enemies. If you stand near his leg, he can do nothing. --- Official Lightning's shorts and Selphie's panties of every board. Official Kairi's panties and Aqua's shorts of KH3 board.
Yeah Flexile, Old Dragon Slayer, Pursuer, and Dragon Rider were all pretty easy. These are early bosses though. I didn't have any trouble with a few bosses. Freya managed to get me with an errant leg but that boss isn't bad. I didn't have too much trouble with the Mirror Knight. It got a little hairy during the summons but nothing too bad. Though I guess I wouldn't say he was easy.