Mewtwo vs Yveltal

This is something I was thinking about while talking to Twili. Instead of Mewtwos current crappy Mega X Evolution, what if it had become this instead? In this story I'm using the Mewtwo from Mewtwo Strikes Back. The Mega Evolution itself is a Dark/Psychic typing, and Psystrike has become Psyshadow, a move that's become a dark type version of Psystrike with the added effect of increased critical chances. Enjoy!

Yveltal launched another Oblivion Wing at Xerneas. It wasn't doing much, but the more effort Xerneas had to use to dodge the slower its dodges became. Yveltal smiled, this wouldn't take long. Destruction would finally snuff out Life completely, and nothing could stop it. Not Xerneas, not that pink rock Diancie, NOTHING.

Yveltal was about to launch another Oblivion Wing against Xerneas, but was stopped as an Aura Sphere smashed into its back. It turned, angered as to what might even dream of interfering with the God of Destructions fun. As the smoke cleared it would become clear that the sphere had come from Mewtwo, the very same Mewtwo originally created by those scientists so many years ago.

Yveltal screeched at it, "Why? Why do you interfere!?"

Mewtwo held its arms outstretched and glared back at the Destruction pokemon. "I sensed a power, a power that would endanger pokemon everywhere. I couldn't allow this power to run rampant."

"Who are you to claim this responsibility?!"

"I am the defender, the protector of every pokemon on this earth. I am Mewtwo, and if you wish to harm any of the pokemon of this world, then you must destroy me first!"

"Then I shall scatter your ashes to the wind!"

Yveltal threw an Oblivion Wing at Mewtwo, who dodged sideways but took a full frontal charge from it in return. Mewtwo grunted from the force and flew backwards before righting itself and throwing a barrage of Aura Spheres at Yveltal. Yveltal took the brunt of the attack as dust and smoke filled the air. Mewtwo lowered its guard for only a second, but it was enough. An Oblivion Wing slammed into it full force, sending him plummeting towards the ground.

Xerneas meanwhile looked on, gathering its strength to join in and help the new ally that had arrived. Yveltal scoffed at Mewtwo. "Easily taken down, pathetic." It turned its attention back to its opposite and readied another Oblivion Wing. "This is the end old friend." However, once again it was stopped, this time as Mewtwo crashed into it with a Psychic enhanced rush. Though Mewtwo had staggered Yveltal it was clear that the Oblivion Wing had done considerable damage to it, it floated huffing for breath as Yveltal turned and bellowed at it.

"Why won't you stay dead?!"

It charged yet another Oblivion Wing, but Mewtwo threw an Aura Sphere at which it was forced to dodge before Mewtwo again rushed it, slamming into it and sending it reeling yet again. It roared its anger and abandoned Oblivion Wing, instead it opted to use its better manuverability as it began to glow and in a flash began striking Mewtwo again and again with Sky Attack. Mewtwo, already badly damaged lost what little strength it had left, and went limp kept aloft only by Yveltals continued assault. As Yveltal finished its barrage and watched as Mewtwo plummeted to the forest below it let out a bellowing laugh.

"Yes! YES! Now you see! Now you all see! Destruction shall reign, this world will become ruin! Charred, blackened, and turned to ash beneath my power!"

As Yveltal continued its speech above Mewtwo lay in a heap on the forest floor. Several pokemon surronded it, terrified of Yveltal, but more concerned with the one that claimed to be their protector. A Caterpie approached Mewtwo and gently nudged it. "Come on, you can't give up yet, we're all counting on you. Please don't give up." The other pokemon agreed, giving encouraging words to Mewtwo, willing it to get up.

Yveltal looked down upon the scene in disgust. "Pathetic, and weak. I will release you from your pathetic lives!" It readied an Oblivion Wing, prepared to destroy the entire forest starting from where Mewtwo and the other pokemon were. Xerneas' eyes grew wide with shock, and it screamed. "NO!"

As all of this was happening on the outside, inside, something was stirring in Mewtwo. The compassion that the pokemon had shown for him, willing him on unlocked something that no one knew existed when it was made. Only recently had the human Sycamore even begun research into what was now known as Mega Evolution. A shine originated from the core of Mewtwos being as a light engulfed it.

Yveltal unleashed its Oblivion Wing upon the pokemon as it laughed maniacally. As it reached the tips of the trees however a dark barrier stood in its way, blocking the attack completely. A new figure rose from the forest. Black where there once had been gray, blue where there had been purple. Its tail had grown sharper, its small blunt horns hard sharpened and curved, along with that sharp pointed spines had grown from its back, curved upwards. The balls on its hands had slimmed, and its feet had arched even more, the ball removed and they now ended with a sharp spike, more akin to a demon.

As Mewtwo rose to become level with Yveltal it opened and glared at Yveltal with its glowing purple eyes. Yveltal flinched backwards not sure what this new thing was, unknowing that it was Mewtwo itself.

"Who...What are you? What happened to the other one?"

Mewtwo simply stared at the Destruction pokemon, eventually it spoke, its tone deeper, and more menacing. "I've told you, I am the protector of pokemon everywhere. I am Mewtwo, and I will stop you." It said nothing more as it charged forward slamming into Yveltal yet again, and their battle was renewed.

Xerneas had turned its head as Yveltal unleashed its Oblivion Wing upon the innocent pokemon, more life wasted, it thought. It, however, was shocked to see the new form this new pokemon had taken. Mewtwo had Mega Evolved, and now they stood a chance of stopping Yveltal! Meanwhile, Diancie had awakened from its slumber, and sensing that Yveltal was free once more had begun racing to the location of the battle.

In the sky Mewtwo and Yveltal were evenly matched, Oblivion Wing smashed into Mewtwo, who shrugged it off and threw Aura Spheres back at it in return. They slammed together and then broke apart, both giving each other plenty of ground. Mewtwo drew its hands together and raised them above its head. A dark psychic energy gathered there, and it released it sending several dark arrow type projectiles at Yveltal. This transformed Psystrike crashed into Yveltal who gave a loud grunt of pain as it climbed higher into the air, out of the smoke. Mewtwo followed it with its gaze before charging after it.

Diancie had finally arrived and was watching the battle unfold alongside Xerneas. Xerneas turned to its fellow Fairy type and began to speak.

"Diancie, we must hurry, I don't know how long Mewtwo can keep Yveltal busy."

"Mewtwo? That is Mewtwo? What happened to it, I don't remember it looking like that from the legends."

"There was some kind of light, and it rose to face Yveltal in that form. I believe Mewtwo has Mega Evolved!"

"Amazing...but yes we must hurry."

Diancie and Xerneas began to focus their energies together, gathering power to form the coccoon that would hold Yveltal yet again. Meanwhile, Mewtwo had gained no ground over Yveltal, nor had Yveltal gained any over it. They were equally matched, battling it out amongst the clouds. Mewtwo would attack, and Yveltal would retaliate. There was no end to this battle, and if it did not stop soon destruction would indeed happen. A shout came from Diancie below.

"Mewtwo! You must bring Yveltal to use! We can stop all of this!"

Mewtwo glanced down for but a second, and suffered for it, getting blasted with an Oblivion Wing. It shook its head as it recovered and blasted full force towards Xerneas and Diancie, with Yveltal in tow. As Diancie and Xerneas readied the blast that would incase Yveltal, Mewtwo twisted and faced Yveltal, blocking an Oblivion Wing and sending another Psyshadow at it. Yveltal blocked most of the damage, but that wasn't the aim of the attack.
By sending out that attack at the right time Mewtwo had created a smokescreen, and while Yveltal had no clue what was going on Mewtwo had moved out of the way as Diancie and Xerneas unleashed their power. The smoke cleared just in time for Yveltal to see its prison coming straight for it. It screamed in rage as its power was once again contained within the diamond.

In the aftermath Diancie had taken the cocoon and hidden away, hopefully this time where no human would be able to find it. Xerneas and Diancie both thanked the now normal Mewtwo, and returned to their places. Xerneas to take its place in the forest, and Diancie to return to its slumber. Mewtwo in the meantime would return to its cave and its pokemon family. With this new found power he would protect all pokemon that were threatened by destruction or any other force that would dare harm them. Mega Mewtwo would be the legend evil pokemon would fear.