In Pokémon Legends: Z-A, Galarian Yamask needs to meet certain conditions to evolve into Runerigus. It just needs to take some damage before you stand under one of two specific bridges in Lumiose City, so the hardest part of evolving it may be catching it in the first place: Galarian Yamask can be caught in Hyperspace Lumiose, and when it shows up is at the luck of the draw.
