Today's Pokémon Smash has announced a new Pokémon - although all we know about it is a picture and that it is somehow related to Mewtwo. The blurb on the main site describes it thus:
The mysteries of Pokémon X and Pokémon Y continue to grow with the unveiling of a Pokémon that is strangely familiar! It looks a lot like the powerful Legendary Pokémon Mewtwo, but not quite the same… This new Pokémon shares many traits with Mewtwo, including a light-purple body and piercing, powerful eyes.
From this blurb, we can safely assume that it isn't a Mewtwo forme, so is probably a relation much like Mewtwo is to Mew - a Mewthree, perhaps? The official site also has a YouTube video with this new Pokémon in action - as well as brief looks at Genesect, Cloyster, Rampardos, Gyarados, Machamp, and Zangoose in battle - you can find that video after the jump.
We've also got a tip that says that this Pokémon, and Mewtwo itself, will appear in a trailer for the 16th Pokémon movie, Extremespeed Genesect: Mewtwo Awakens on April 18th - hopefully with some more information on this Pokémon and its relation to Mewtwo!
We've got literally no information other than this on this new Pokémon - not a name, not a type, not any description whatsoever other than what we have quoted. If we do get any more information, though, you can be sure we'll be updating our Cryptidex page with anything we find.