Belphegor (Bravely Default)

Strategy
Start the battle by examining the boss! Despite its level, Belphegor is not an easy nemesis to reckon with, as it can change it's weakness from one thing to the next when it is damaged. Making the boss more of a difficulty: Hit it with the wrong attack, and you'll be helping it instead of harming it. The same thing applies to the Floating Spheres that it summons. At lower levels in the game, it is recommended that you recognize who has what class, and who attacks in what order. Once you get to higher levels, you can just devote one of your magic-affiliated classes to do the job while the others take care of the spheres. Though the fight may not be worth the JP that you get in the end, it gives you a good idea of how to work with classes and characters deeper than just "Firing everything" at the enemy.