Mephisto

Mephisto (めふぃすと Mefisuto), known as the Phantom of Darkness is Demon that was previously under the control of Zeref, but now belongs to Dante Royard via Take Over. He was weakened during his fight with Deliora and had tried to take over Dante, but was defeated and his power is now under the control of Dante. He has, multiple time, tried to regain control and free himself and has nearly succeeded, but has been defeated. He harbors a mutual hatred of Deliora. Both of them had been the reason for Gray's parents' deaths as well his masters' death. Because of his small stature compared to his rival, he has never been seen, which had led the people to believe Deliora had been the cause of it.