Beelzebub is the true final boss from Caladrius.
Beelzebub is a fallen angel and demon lord who rules over Gluttony out of the Seven Deadly Sins. Despite having being trapped in the underworld eons ago, she actually got tired of fighting and now spends eternity in complete idleness. When the gates of hell opened due to the misuse of the forbidden spell, Beelzebub was able to step into the human world. She has no particular goal and cares little about humans, seeing them as little more than ants, but still enters the human world merely out of boredom, expecting to taste some humans after such a long time.
Beelzebub can only be fought if the player reaches and defeats the regular final boss, Graham Galadis Baladin, without using continues, after which the player character is greeted by Beelzebub and then taken into the final stage. Upon being defeated, Beelzebub retreats into the underworld, but promises to return should the gates of hell get opened again.