[Update]: Just as we all suspected, this new Legendary Pokémon is some sort of transformation of Mewtwo.
There's no word yet on what the pocket monster's name will be, but the description for the video points out its obvious resemblance to the classic psychic creature Mewtwo. "Get a glimpse of a newly discovered Pokémon in Pokémon X and Pokémon Y that bears an intriguing resemblance to the Legendary Mewtwo!"
What do you think of this new addition? More importantly, what do you think this Mew-esque monster should be called? Sound off with your thoughts in the comments below.