Just found amazing resource dedicated to slavic paganism. Honestly, for me, grown in Russia, this reading was full of discoveries. Just two quotes:
Koshchei. Koshchei the Deathless for his supposed invulnerability; noted for being the abductor of beautiful princesses. He is a powerful wizard or demigod who gains immortality by keeping his fiery soul hidden. He kidnaps Marena (Mara, Marya Morevna), the Russian goddess of death. He tells her the location of his soul, which she tells the story’s hero (usually a son or husband: Dazhdbog, Prince Ivan, Prince Astrach, etc.). Koshchie is the son of Vij, lord of the Underground, and travels on a war-horse or as a whirlwind.
Marena, Mara, Marya, Morevna. Russian winter- and death- goddess. In one myth, she is a sorceress and enchantress who turned the sun-god Dazhbog into an ox. She refused to change him back until his father Perun agreed that they should marry. However, she later left him for Koshchei, son of the Underworld lord Vij. They conspired to kill Dazhbog, who was searching for her. She drugged him, and Koshchei threw him down a well. Finally, she nailed him to a mountain in the Caucasus, but the goddess Zhiva rescued him. Dazhbog finally had his revenge.
Despite this unsavory tale, Marena survived into Christian times as St. Mary, the consort of St. Ivan, who is Dazhbog.
And surprise! Something I wrote in screenplay is really have much in common with some concepts explained there, while I really thought what I devised it by myself! If you are someone who wants to dig deeper into Story, than that page is for you. Happy Halloween. 😉