The spirit inside of the rune stone has taken a form resembling that of Nidhögg, from norse mythology, which also allows it to fly through the air and watch from above, as it looks out for weakened souls to absorb in order to grow stronger. Due to how powerful the transformation was, the stone has begun to split and crack, with the exception of the tail stone, which is the one Galarian Yamask is carrying. On the head is a pair of false, glowing eyes, that are supposed to represent Valhalla and Hel, two places of afterlife. The extended fifth finger on it's hands are reminiscent of those on pterosaurs.
by mynamissketch