Dark Emperor (Final Fantasy)

The Dark Emperor is the dark half of Emperor Mateus's soul and the final Boss in Final Fantasy II. In contrast to the game, the novel version of the Dark Emperor is the final form of Satan, who had been controlling Mateus in this incarnation.

Story
After getting into Palamecia's mountain-protected castle, the party confronts the Dark Knight. Before they can do anything, the Emperor reappears, in this form. By killing him, the party only made him stronger, as he has now gained incredible strength and became Emperor of Hell. Ricard Highwind summons the Wind Drake to get the party out of Palamecia while he confronts the revived Emperor. The Emperor kills the Dragoon easily.

Summoning the castle of Hell, Pandaemonium, where Palamecia once stood, the Emperor intended to reign over both earth and Hell. However, the party traveled through the Jade Passage and confronted the Emperor head on. He is eventually defeated, and returns to Hell.

Powers and Abilities
The Dark Emperor is much more powerful than when he was just Emperor Mateus. The Emperor gains the ability to summon Pandaemonium to the surface world as well as a slew of new demonic powers. His physical attacks have a drain effect, allowing him to steal lifeforce from enemies to replenish himself and heal injuries.

His physical strikes sometimes poison or stun whom they strike. His Thunder spell has been enhanced and has gained a high level Flare attack and the original Meteor spell, Starfall as well as many status ailment spells. The Emperor is nigh invincible to most physical attacks unless it's against the Blood Sword or the attacker is augmented by Haste or Temper, and he is immune to all elemental magic and almost any attempt to inflict status ailments on him, with the only known method to do so being the Cursed Sword.

His Dark Half was also shown to generate purple flames of what was presumably hellfire, as evidenced by his encounter with the party in Castle Palamecia where he attempted to use it to kill them. Similarly, even the mere act of returning from Hell to the living realm causes noticeable distortions, where the environment flashes with shades of purple.

Dissidia Final Fantasy
The Dark Emperor appears as Emperor Mateus's EX Mode.