Darkrai finds a Mega evolution stone and turns into the overlord over all pokemon. He traps Mewtwo, previous pokemon ruler under his spell and had became Mewtwo X. Mewtwo X over see's darkrai. Like his right hand man. And in Order to Stop Darkrai and Save the Save the World, J and His Pokemon Team (Charizard, Greninja, Raichu, Crobat, Aerodacyyl, and Tyrantrum) must Find Mew