Pokémon the Movie: Diancie and the Cocoon of Destruction

In the underground Diamond Domain, where many Carbink live, the Mythical Pokémon Diancie serves as ruler. The Heart Diamond that sustains the land is beginning to fall apart, and Diancie is not yet strong enough to create a new one. When thieves awaken the Legendary Pokémon Yveltal from its cocoon in the process, Diancie embarks on a journey with Ash and his friends to meet Xerneas and discover her true power. Can they stop Yveltal's rampage and save the Diamond Domain?