What I did was go into the fight with four dragoons and used jump every time. Within two to three moves the boss would kill me. Finally I did some research and seen that you can access a shop and buy 8 Air Spears (I'm sure that's not what they are called but it is something like that) and that was the monsters weakness. I went into battle and noticed the damage was just increasing every time I jumped. Finally after around 10 game overs I won. The boss is hard and unexpected.