According to IGN, Greninja and Ash will form a kind of an unshakable bond which will further help them to progress in the game. Reports indicate that they will also feature Pokemon X and Y along with Pokemon Z in anime. According to the rumors, the game will be launched next year while Pokemon X and Y will be released back in 2013. Meanwhile, Pokemon Omega Ruby and Pokemon Alpha Sapphire will be released last year.
The rumors further indicate that Zygarde will be included in the game in all its five forms. This will include cell, blob, dog, snake and Mega Evolution, all of them to be included in the game.
All of the Pokemon X and Y along with Pokemon Z are related to Norse Mythology. Zygarde will actually start in a blob form which is also known by the name Zygarde Core. This core will further form the base of all the proceeding forms of the Pokemon. This will further involve into a Zygarde Cell, which comes in the form of a flat green blob.
Stay tuned for more updates on Pokemon Z!