Here are the trailers for the 13th Pokemon movie Ruler of Illusions Zoroark:
So, apparently, Zorua and Zoroark are partners in crime, and are most likely chasing after Celebi. I assume it's for some random bad guy, who's probably manipulating them or something. After all, no Pokemon are truly bad. ;(
And, as I suspected, Zoroark is the "evil Ash" from the first trailer. Now it's revealed he "is" also Entei, Raikou and Suicune (I personally think that's better than actually figuring out a reason to put all the three dogs together in one movie) . Makes sense: according to Japanese mythology, foxes (or "kistune") are shapeshifters. I don't think Zoroark will know Transform in the games, though. But it's cool nonetheless.
So far so good.