Mewtwo is the eternal badass of the Pokémon universe. I don't care what generation you entered the series from or how much you think psychic Pokémon are unfairly overpowered, we all have to agree that this guy just emits an aura that demands respect every time he hits the battlefield.
Fans went crazy over the new Shadow Mewtwo when it was first announced for the Bandai Namco's arcade fighting game Pokkén Tournament, so much so that they want him to be canonized as an official Pokémon and brought into the actual game. When asked by Polygon about this, Producer Masaaki Hoshino gave a non-committal answer. He also works for Bandai Namco and can't speak for The Pokémon Company.
"When we were originally coming up with the design, we worked very closely with The Pokémon Company and Game Freak to make sure everything was right. What happened was, we at Bandai Namco had the idea of making a really cool dark-colored Mewtwo, so we had one of our designers take a crack at it and then presented that to The Pokémon Company and Game Freak. They all thought it looked really cool, so then we worked together to brush it up.
Because everyone really liked Shadow Mewtwo, I have a personal hope that they'll continue to use it, but it's not really our decision, unfortunately."
Tekken producer Katsuhiro Harada also was unable to confirm anything.
"For this game, it is kind of a spin-off from the main series. It takes place in this area called the Ferrum Region, which means something like 'Iron Region,' playing back into the Tekken connection.
So, within the context of this spin-off, [Shadow Mewtwo] is obviously a canonical character. Of course, how The Pokémon Company and Game Freak decide to use the character is up to them, but I think Mr. Hoshino's passion for the character might inspire them and encourage them to use it!"
In other words, it's out of Bandai Namco's hands. Shadow Mewtwo would definitely make a worthy addition to a future Pokémon game, but only time will tell if The Pokémon Company wants to. Write to your local congressman, or maybe just The Pokémon Company itself, and let them know you want some Shadow Mewtwo in your X and Y!
Maybe we'll even see him in Z… if it ever comes out. Check out 15 new minutes of Shadow Mewtwo footage in English below.