Pokemon Sun & Moon - episode 52 - 29 Nov, 2017

Our heroes are all gathered at the Altar of the Sun, along with all four of Alola's Island Guardians. Lillie and Gladion ask the Island Guardians for help to rescue their mother. Tapu Koko and the others perform a ritual that enables little Nebby to evolve into the mighty Solgaleo—one of the Legendary Pokémon of Alola! At Solgaleo's invitation, the Pokémon School students climb onto its back. The Island Guardians upgrade Ash's Z-ring into a Power Z-ring, and with the help of a new Z-Move, Solgaleo opens an Ultra Wormhole and carries them through! (Source: Wikipedia)