Baltoy are stylized pottery given life in ancient times to use their psychic powers in order to accompany great kings to the underworld. Yet when buried with them, they found themselves not in the afterlife which the priests had promised them, waging glorious battles commanded by the spirit of their king, but stuck in the dirt next to skeletons or encased in elaborate tombs. The afterlife, if there is such a thing, is not something a live pokemon can enter, no matter the ritual used or method of burial.
And thus the Baltoy had no choice but to escape, and took to moving dirt slowly with their minds. This method is next to useless, but some Baltoy colonies have failed to discover the alternative. Every now and then they succeed, escaping to dry land and unveiling a major archaeological discovery from thousands of years ago. Yet while Baltoy were intended by their creators to be psychic pokemon, they were also made from baked earth and carry within themselves the power of ground pokemon. When a Baltoy learns to channel this ability, they start to dig like Sandshrew if not Diglett. They share this information with its neighbors and escape to the surface, often via a roundabout route to hide the location of their burial.
However they break free, they find themselves in a world changed beyond recognition. More often than not, they gravitate to the ruins of the society that built them, and strive to protect their heritage instead of their kings. Perhaps this was what their builders intended all along, and the stories of helping kings fight in Heaven were merely a way to convince the people to make pokemon which would preserve their history.