Well, I'll admit that I'm a bit disappointed too, but the fact is, this is kind of huge. Whether or not this is a new forme or a new Mew in general just provides a sense of nostalgia to the original Mews of generation 1. However, does anybody else think that this thing can't just be a Mewthree? I mean, I'm probably getting ahead of myself here, but let's look at the video. All of those attacks obviously show that this thing has major powers, not only that, but that ring around its head and the head tail thing, along with the oddly shaped horns... Screw it, I'll cut to the chase. Anyone else think that this is an experiment with DNA from Arceus too? I'm probably wayyyy off base here, but still.
Either way, I do look forward to the explanation they give for him. He almost looks otherworldly, so maybe something from space? Anyway, I just hope that they don't give him the "distribution" treatment that they've been giving for Pokemon like Keldeo or Genesect. Even if it is just an event, I want some sort of explanation for what came to the creation of this being in the form of some sort of sub plot and a battle, and not just walls of text.
With all of that said, we can pretty much all agree that X and Y has a heavy emphasis on genetics of some sort (heck, the Japanese titles have DNA in the logo!), and the fact that they showed Sylveon a couple of months along with this kind of screams some sort of DNA Splicing sub plot, or even some sort of mechanic. At least to me anyway.