In Galar, Yamask has a Ground/Ghost-type regional form. It evolves into Runerigus when the player travels under the stone bridge in Dusty Bowl after Yamask has lost at least 49 HP from one attack and did not faint in the same battle or since.
Yamask is a shadow-like Pokémon holding a mask that has a face from its time as a human. It has two shadowy, tendril-like arms and large, red eyes. It also has a small tail-like appendage that holds the mask. Yamask is capable of speech when possessing a human, but not in its regular form.
Due to being a human long ago, it has memories of being a human. If someone wears the mask Yamask carries, they will become possessed by the Yamask in question. Sometimes, it looks at this mask and cries, apparently in longing. Yamask is known to wander the ruins of ancient civilizations.
The Yamask of Galar have purple eyes and a small piece of an ancient stone tablet is directly attached to its tail. The tablet bears cursed engravings, and is said to be absorbing Yamask's dark power.
Yamask debuted in A Night in the Nacrene City Museum!, where it was causing havoc in the Nacrene City Museum. This eventually turned out to be because Yamask's mask had been put on display after it accidentally dropped it while sleeping. In the end, Lenora, along with Ash, Iris, Cilan, and Hawes gained an understanding with it and gave its mask back. Yamask then left the museum peacefully.
Galarian Yamask is the only Pokémon to have a location-based evolution in Pokémon Sword and Shield, as all others are either unobtainable or use an Evolutionary stone to evolve instead.
Yamask is the only Pokémon introduced in Generation V to evolve into or from a Pokémon introduced outside of said generation, though only its regional form is capable of this.
Origin
Yamask is based on an Egyptian šwt holding a death mask. Galarian Yamask holds a clay tablet based on Ingvar runestones instead.
Name origin
Yamask may be a combination of 闇 yami (darkness), や ya (bad), or Yama (lord of the dead in Hindu and Buddhist mythology), and mask.
Desumasu may be a combination of death and mask. It is also a pun off of ですます体 desumasu-tai, a form of polite Japanese which gets its name from the fact that sentences often end in です desu or ます masu.
This Pokémon article is part of Project Pokédex, a Bulbapedia project that aims to write comprehensive articles on each Pokémon species, as well as Pokémon groups and forms.