Every since the Mewtwo like Pokemon was first revealed, there has been a lot of speculation as to what exactly he is. Some sites have suggested it was simply a new form of Mewtwo (which is becoming increasingly common in Pokemon), where as other sites merely assumed it was an evolved form of Mewtwo. However, thanks to a scan from Coro Coro and the fine folks at Serebii, the Pokemon is confirmed to be a new form of Mewtwo.
Despite this less than exciting development, it’s interesting to them do more things with the older generations. Hopefully there will be a special quest or event to get this Pokemon, but only time will tell.