>>41480391Because Yamask is being possessed. When it evolves it's fully absorbed:
>Galarian Yamask (Sword): A clay slab with cursed engravings took possession of a Yamask. The slab is said to be absorbing the Yamask's dark power.>Runerigus (Sword): A powerful curse was woven into an ancient painting. After absorbing the spirit of a Yamask, the painting began to move. I would reckon that if it weren't for Perrserker, they probably wouldn't have minded making it count as "Galarian Cofagrigus," but since Perrserker is very different from Persian, they didn't want it to be an outlier and thus made 2 regional split evos.