Pokémon S12E24 - Pillars of Friendship!

Pokémon Hunter J arrives in Snowpoint City and targets the legendary Pokémon Regigigas, which is sleeping inside the Snowpoint Temple. After J commands her henchmen to launch an attack, a maiden from the shrine asks Ash and his friends for help. But Ash and the others come too late; Regigigas has been reawakened and starts rampaging.