Shadow Mewtwo is quite a big deal in Pokkén Tournament, at least in terms of marketing. Revealed last year with quite a bit of hoopla (not Hoopa, that's different) the character will even have its own amiibo card included in pre-orders and first-run copies of the game.
That prominent role in the upcoming fighting game doesn't secure its place in Pokémon canon, though. Developer Bandai Namco has been chatting to Polygon about the character and acknowledged that its inclusion isn't indicative - as far as it's aware - of a broader role. The game's producer, Masaaki Hoshino, said the following:
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 veteran and fellow Bandai Namco game maker Katsuhiro Harada also pitched in, acknowledging that the new fictional area in the game - the Ferrum Region - could give Game Freak and The Pokémon Company room to ignore the character in future, though if Shadow Mewtwo is popular with fans that could boost it's prospects.
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!
The Pokémon Company, intriguingly, has simply given a 'no comment' on the question of whether Shadow Mewtwo is canon. Either that's a surprise for a future time, or Game Freak simply hasn't decided yet.
Let us know what you think, and keep your eyes peeled for our Pokkén Tournament preview later today.