Notes:

Again, this looks fake, but still has the possibility of being real. It kind of looks like he Pokémon in the champion's room, so there's that.

EDIT
Okay, so apparently, the Pokémon's name is "Seradin,"
It looks like a Fairy/Ghost type, and has a striking resemblance to Champion Diantha. This is the only image so far of it, and nothing else is known about it.
My hypothesis if it is real, this Pokémon will have some kind of connection to Diantha, and will probably be what the event is about.

ANOTHER EDIT
Well, after doing my research, I have my doubts, being the earliest use of this image dates back to September 27th. However, this still has some credibility, being that the earliest copies of X and Y were released on October 2nd, 5 days before. This picture may have been taken by someone that is either with or knows someone that is with the production of Pokémon X and Y, because there isn't any other way to take this picture, unless given good editing skills. Also, since this photo was used on September 27th, no one knew who or what the champion looked like, so unless this is a huge coincidence, I'm still leaning towards both ends.