Pokémon the Movie: Diancie and the Cocoon of Destruction

When the Mythical Pokémon Diancie cannot figure out how to make a new Heart Diamond to save her kingdom of Carbink subjects, she seeks out the Legendary Life Pokémon Xerneas for help, meeting Ash, Serena, Clemont, and Bonnie on the way, as they help her escape a group of jewel thieves and the unintentional awakening of the Legendary Destruction Pokémon Yveltal.