Behemoth

Appearance
When released from the seal, he had a liquid black shape with sinister glowing eyes. After finishing all Elementals and the remaining Undead, the devil materialized. Its black, hardened body was reminiscent of a seasoned warrior, or a wild beast. Its face was covered with a golden mask, and it seemed to still be in agony somehow.

Plot
Behemoth is a devil of a bygone era. It was sealed for many years, perhaps hundreds of years. When he was released, he devoured demons, elementals, cadavers and living humans without discrimination to recreate his body.

Abilities
He was powerful enough to create a crisis across the continent. Even an attack with all of Luna's power before her awakening didn't have much effect on him.

Trivia

 * After defeating him Luna acquired a black coin.