Pokémon the Movie: Diancie and the Cocoon of Destruction

In the mystical underground realm known as the Diamond Domain, Diancie reigns but faces a dire crisis: the Heart Diamond, vital for the land's survival, is deteriorating. Lacking the strength to forge a new one, Diancie seeks the aid of Legendary Pokémon Xerneas. However, a band of thieves with sinister intentions intervenes, inadvertently awakening Yveltal from its slumber. Ash and his companions must rally to assist Diancie in unlocking its hidden potential, halt Yveltal's destructive path, and protect the Diamond Domain from impending doom.