You already said its fake...that was also a dirty trick.
Actually they are similar, not the same. They are a few shades off from one another, not the same colors. Also Gamefreak debunked the relationship. Ditto was made before Mew. Mew itself was a gag and introduced without many people knowing once the games were finished. Mew itself was never supposed to exist, which is why a few of the early games have the Mew Glitch. Ditto on the other hand was designed based after a smiley face. Ditto can transform into any Pokemon because all Pokemon have a face. *Latter half is me not GF*
Mew can trasform because of the supposed Ancestor thing. Ditto can transform because all pokemon have a face. See above for full details. XD
I'm really hoping it's a new Pokemon, forms are pretty boring. I'd only be okay with it being a form if it had something to do with the Berserk Gene. But, then again, event (I'm assuming it would be an event..) Pokemon that never leave my box are pretty boring anyway, so....
But for now I'm calling it Mew-Z because it looks like a modified Mewtwo, making it similar to the Porygon family, (Name, Name 2, Name-Z) each being a modified version of the previous one and would also give us the Z to our X and Y. ;P
The reason for Kyurem to be called new Pokemon actually makes a lot of sense. Kyurem is also the only Legend to have stat changes thanks to Reshiram and Zekrom. Only other Pokemon that does that is Rotom thanks to the appliances he takes over.
As for names, I'm hoping they do something a little more original than Z or a number. They most likely won't but still I hope they do.