Beelzebub is a boss in Bravely Default that can be encountered as a Nemesis in Norende Village and is based on his appearance in Final Fantasy: The 4 Heroes of Light.
Beelzebub's attacks include Octowhip, a physical attack that hits the entire party, and Firaja, a powerful fire-based attack that is an absorbable genome. Demon Eye inflicts everyone with a combination of Dread, Confuse, and/or Stop.
His specialization is the use of Gluttony, where he absorbs all damage for four turns. At this time, Beelzebub can still attack with Tentacles, which physically damages one character. At the final turn of Gluttony, he will attack with Acid Breath which hits the whole party and lowers both their physical and magic defense to the lowest possible level. If Beelzebub absorbs enough damage during Gluttony, around two-thirds of his max HP absorbed, he will Overflow and heavily damage himself for more than the amount of damage that was healed.
The battle can either be quick or time-consuming. The first method involves dealing a large amount of damage when Beelzebub is not in is Gluttony form. This can be tricky when using a Spiritmaster's Stillness every two turns with the Hasten World passive ability. One would have to time it so the Stillness fades on the very same turn that Beelzebub exits Gluttony.
The other method involves damaging him while undergoing Gluttony by dealing enough damage to him in that state to cause him to Overflow and harm himself. One way to do this is to make all the characters use the Freelancer job and make them as fast as possible and give the slowest character Hasten World in place of Speed 20% Up. The player should set them up with the Martial Arts job command, engage in a separate battle, and use Phoenix Flight to reduce their HP to 1. After that, the player should swap out Martial Arts for Spiritism, for the slowest, and Medication for the others. Finally, one should stock up on (or grind for) Demon Tails and Dragon Fangs.
The tactic is to use Compounding and create numerous Dark Breaths, which deal damage equal to the user's Max HP minus their current HP (or Max HP minus 1, in this case). The faster characters should compound a Dark Breath and use Mimic three times. The slower character should use Mimic, then Stillness. Mimic will duplicate the effect of Dark Breath, but will not consume the items required, expending 3 of both items per two turns. This method is expensive, but is one of the faster ways to deal with Beelzebub.
Beelzebub [+] Edit
A more difficult version of Beelzebub is encountered as a Nemesis with heavily increased stats.
Beelzebub means "Lord of the Flies" in Hebrew and is a name often associated with the devil. It appears in the book by William Golding of the same name (Lord Of the Flies) as the head of a slaughtered pig on a stake. Beelzebub is also one of the Seven Princes of Hell, associated with the deadly sin of Gluttony.