Agoyon

Naganadel debuted in SM084 in Ash's Poipole's dream. It made its physical debut in SM089, where it encountered the Ultra Guardians after they arrived in its home world with Lunala's help. After being healed, Naganadel telepathically told everyone how Necrozma lost its light saving the world from a meteor, causing everything to become a dark and barren wasteland. Afterwards, the Ultra Guardians decided to help restore Naganadel's world by sharing their Z-Power with Necrozma in order to turn it back to its former self.

In SM090, Naganadel helped Necrozma regain its true form by giving it some of its Z-Power. Once successful, Necrozma turned back into Ultra Necrozma and restored Naganadel's home world to its former glory. As the Ultra Guardians prepared to leave, Naganadel informed Ash that Poipole wished to stay behind and protect its home, much to Ash's sadness.
(Source: Bulbapedia)