It suddenly got very Norse in here.
http://www.nintendoworldreport.com/news/41147/pokemon-new-zygarde-forms-revealed
CoroCoro magazine in Japan has revealed what appear to be the first new forms of Pokémon for the swan song of the 6th generation.
The magazine lists four alternate forms of Zygarde (#718):
These new forms were announced as part of the new season of the anime in Japan known as "Pokémon XY&Z", along with a form of Greninja that appears to be wearing clothing similar to Satoshi/Ash known as the "Satoshi Greninja". As of yet, no game has been announced with these Pokémon, or if any of them will even appear in a game.