Mohn is Lusamine
's husband and Gladion
's father. In the games, he lives on the Poké Pelago, helping the player grow Pokébeans. He had amnesia, and was transported there after going through an Ultra Wormhole. In the anime, he also got lost in an Ultra Wormhole, but is nowhere to be found.
Gladion's Nihilego (Lillie)
resided in the Ultra Space until one day, Mohn
came through an Ultra Wormhole. It caught him before he hit the ground. Realizing that he needed to go back through the wormhole but was unconscious, Nihilego pulled him through and they arrived in the Galar Region's Crown Tundra.
Nihilego lived with Mohn in a cabin in the Crown Tundra for years, since Lillie
was a baby. It took on the look of Lillie
while living there. Mohn didn't know exactly why it wanted to look like her but he guessed its was happy there with him and by looking like Lillie
, he wouldn't have a reason to leave and go look for her. Nihilego was afraid that if Mohn saw his reflection in a mirror it would trigger his memory, so it took off all the mirrors in the house and dirtied the windows. It had stored his old clothes and mirrors away properly, so, Gladion understood that Nihilego really cared for his father.
After Mohn's memory was restored and he remembered his family members, Nihilego was invited to stay with the family and it was caught in a Beast Ball.