The Japanese show Pokemon Smash has revealed a new Pokemon that is based on Mewtwo! The official Pokemon website strongly hints it is a new Pokemon rather than a Mewtwo forme:
It is suspected that the newly discovered Pokémon has some sort of connection with the Legendary Mewtwo—a powerful Pokémon that first appeared in Pokémon Red and Blue Versions.
Given that Mewtwo was a clone of Mew and one does not evolve into the other, it's very likely this new Pokemon will follow the same pattern. Will it be called Mewthree?
A video has also been released with gameplay featuring the new Pokemon: