Runerigus

I have my problems with Cofagrigus, as it’s a sentient coffin that swallows humans and turns them into mummies, but it’s knocked out of the park by its Galarian cousin, Runerigus. Yamask, in either Unovan or Galarian form, is an upsetting ghost-thing, but given the choice of either evolution, it would never be this one.
What the ever-loving eff is it? It’s apparently made of clay slabs with a serpent drawn on them, but it looks like its in eternal agony, begging for its own death.
This deviant has only ever appeared in one game, Sword and Shield, and may it stay there. Shield’s Pokédex entry reads,
Never touch its shadowlike body, or you’ll be shown the horrific memories behind the picture carved into it.