Beelzebub

Beelzebub (ベルゼブブ), (originally named "Beezelbub" in game, but not in the descriptions), first appeared in Castlevania: Symphony of the Night as a giant, rotting corpse boss with no attacks of its own. Alucard battles it in the Inverse Castle, at the Necromancy Lab area, and is an entirely optional boss. It attacks by taking control of the giant flies that are attracted to it. It also releases maggots that can poison Alucard. The battle starts rather easy, because of his legs, which are very easy to hit. The more damage he will absorb, the more body parts will fall down, at last leaving only head and half of corpse, hanging high under the ceiling, surrounded by giant flies. Beelzebub returned as a boss in Castlevania Puzzle: Encore of the Night and in the DLC chapter 9 of Castlevania: Harmony of Despair.

While many people identify Beelzebub with Satan, Symphony of the Night seems to take his "Lord of the Flies" title literally.

Strategy (Symphony of the Night)
A neat trick that makes this boss very easy is to simply stand on the highest platform and spam the axe subweapon at his head, after repeated strikes his head will fall off and his body need only be struck once or twice more to kill him. Some have managed to beat him in a matter of moments and taken no damage in this fashion.

Castlevania: Curse of Darkness
In Castlevania Curse of Darkness, Beelzebub is a combined material from the Unicorns.