>>26654572P.S.: Also, Mewtwo being able to Mega Evolve in the anime basically confirms manga canon
(for movie 16, at least), in which Mewtwo was made adding human DNA to a cloned Mew - cells from Blaine's arm, to be precise.
The reason it can Mega Evolve without a human trainer and stones is because it has come to peace with its own being & identity, meaning it has a strong bond with itself - the part of it that is human already.
I wouldn't say that game canon "confirms" manga canon, too, but here's an interesting easter egg to say the very least: If you catch Mewtwo in HGSS and have it follow you, it's hard to get it used to you. But even with a freshly caught Mewtwo, if you enter Blaine's gym and talk to it there, it will always be super happy and smile brightly.
And that's not even a stretch: other following Pokémon have unique reactions depending on your location, too. Look it up.
