Yamask

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.

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.