The Galarian Yamask has one of the most elaborate evolutionary methods in the entire series. In order to evolve it, the player must allow Yamask to lose 49 or more points of HP and then, with the damaged Yamask, the player must go under the large stone arch in the Dusty Bowl area. Immediately upon doing the latter, Yamask will evolve into it's Galar-exclusive Evolution, Runerigus.
Contributed by PirateGoofy