In Chapter 16 of The Dancing Goddesses, I gathered evidence that the Russian folktale figure Koshchey the Deathless and his attributes constitute a vague remembrance of ancient Eurasian shamanism, strained through centuries of propaganda from the Christian church. His being some sort of shaman explains exactly, for example, how Koshchey can be “deathless” (by surviving shamanic visits to the land of the dead) and yet always die (because the shaman is human like the other villagers). But why does he always die by the destruction of a magical egg that “holds his death”?
Recently I happened on an article about Siberian shamanism that finally explained even the egg. It seems that among the Ulchi and the Amur Nanai, two Tungusic groups in eastern Siberia, shamans were sometimes asked to take in and protect for a while the souls of those in danger, especially the souls of sickly children. Each such soul was set to rest in its own soft pouch in the shaman’s possession, although the soul was thought to go off and spend most of its time in a soft nest on a soul-tree some distance away. In other words, souls were viewed as “separable” property.
Among the Nanai along the Ussuri and Tunguska Rivers (the latter being far to the west in Siberia, much closer to the Slavic heartland), the soul was thought, however, to take “the shape of an egg”, and many of the stories among these groups involved people trying to seize an enemy’s soul-egg so as to gain control over that person. And here we have the exact model for the central story of Koshchey the Deathless and his peculiar demise, once again part and parcel of the world of Eurasian shamanism.
(Ref.: V. Diószegi and M. Hoppál, Shamanism in Siberia (Budapest, 1978), 444-45.)