The Black Devil felt a sudden ignition within himself, a burning desire of hatred and anger, and he knew that he was now able to pull off what he needed to. Of course, he was going to wait down to the last possible moment to let loose. His boot tapped itself several times in the moments of silence between it all, and he felt the sword on his back, Armageddon, being charged up by the second. As a way to pass the time, the Black Devil used the spell Recreation once more, creating a wisp that traveled down his body to heal up some wounds that were still present. This would give him another edge in the attack he was awaiting to use. His gaze shifted itself to behind the Mage, and luckily for him, he possessed no pupils, so the Mage couldn't tell where exactly he was looking. He saw that Elyx was readying himself, perhaps for a distraction fit for the Devil. Once more it was a stand-off between the two, with the Black Devil just waiting and waiting for the perfect moment. And at long last, it struck him. The perfect moment indeed.
Initiating his plan of attack with the Mage distracted, the first thing the Black Devil did was upgrade his current form. Executing what he called "Spirit Merge," the black scales on his body became cracked and slightly shattered in some areas with molten lava seemingly sealed on the inside of himself. The red jewel located at the center of his forehead went inside of him and popped right out at his chest area, the bug-like wings on his back were torn away for enormous tattered ones, and an extra pair of arms thrust themselves out of the bloody flesh to the Devil.
"Hey kid, ever wonder why I'm the first God of Ishval!?" His voice was still that of the deep Black Devil's, but now his appearance was much more monstrous than it was before. In spite of the fact that he called Elyx 'kid', he suspected they were around the same age. And he knew that at this point even if the Mage knew about the attack, there was no stopping it. Not wanting to initiate the attack behind the Mage because it would risk hitting Ignite and Elyx, the True Black Devil decided to jump straight into the action. One moment he was standing there, the next moment he was gone, and at the end of that next moment, he was right in front of the Mage.
The True Black Devil already had Armageddon drawn, but the sword had already shifted itself to be a lengthy double-edged and two sided scythe. All four of the True Black Devil's arms were placed upon the hilt for the maximum amount of strength, and right on to the blade itself was a great amount of Unholy Energy. Without a moment's hesitation, standing between the Mage, Elyx, Ignite, and all of their attacks, the Black Devil took a swing.
"CANTATA MORTIS!"
The blade swung, and anything caught within its path was utterly destroyed. As a display for its power, the air itself created rippling sounds as if being torn through, and in its wake, the blade seemed to cut dimensions and reality, leaving gaping holes of complete blackness in its wake. The flesh of the Mage, and everything else that stood between him and his death, stood no chance to the power of Cantata Mortis. The blade cut clean through the flesh, and the rest of the body was eaten away by the excess Unholy Energy that pretty much jumped right onto the torn flesh of the cut. In just a short amount of time, the body of the Mage was not just dead, but had completely vanished from existence, and in the path of the cut for the blade of Armageddon was a tear between reality and nonexistence, looking like the environment itself had been cut through and only left blackness. Not only that, but the entire side of the Mystic Tower that was facing the cut had slowly started to crumble right to the ground, unleashing the light of day from the ruins of about half of the Mystic Tower's second floor. With the Mage no longer in existence, and the attack finished, the Black Devil gave it a gentle swing, extinguishing all of the Unholy Energy located on the blade, returning it back to its broadsword form, and sheathing it on its back. The only effect of it that repaired itself was the rip of dimensions, the blackness sealing itself shut for the world of reality once more. It was a phenomenon not even the Black Devil could explain. And there he stood, scaled, molten, and monstrous.
"And that's that."