Dirty Old Man

Question: Why don't the Slavs have a write up for Kotzchei? He seems a perfect midlevel antagonist or potential guide.

I actually did consider adding Koschei as an antagonist; like many other Slavic figures that were super cool, he ended up just getting cut for space (there are a LOT of Slavic antagonist options - Rugievit, Porenut, Porevit, Pripalega, Podaga and the Simargl all ended up on the chopping block, too). But you're right - Koschei the Deathless, in all his ugly old-man glory, is a great mid-demigod antagonist and could be a fun guide as well, particularly if you like saddling your PCs with hilariously antagonistic guides (god knows we do). So, ask and ye shall receive: here was my writeup for Koschei, still hiding on my hard drive.

Koschei the Deathless
AKA: Kaschey, Kosciej, Kostej, Tzar Koschei
        The terror of countless generations of Russian storytellers, Koschei the Deathless is an ancient sorcerer, a lesser immortal nearly on par with the least powerful of the Bogovi themselves. Unpleasant and tyrannical, he terrorizes the lands of the Midnight Kingdom whenever Perun is not on hand to frighten him into submission, stealing livestock, livelihoods and loved ones as the whim takes him. Though he has been known in the past to occasionally foray into the World to seek treasure or particularly tempting maidens (for which he has a weakness), such trips are infrequent; he has a historically rocky relationship with Baba Yaga and the two are seldom getting along well enough for her to allow him through Domkura.
        Koschei usually appears as an old man, extremely bony and angular with a hideous deathly grin and wild, unkempt black hair. He seldom bothers to wear clothing, enjoying the shocking effect his ugly naked form has on others, and is most often found riding through the countryside on stolen horses, which he urges to ever greater speeds until they collapse. When he chooses to set up a semi-permanent residence, he usually favors caves or dank, stony castles, most often in poor repair thanks to his lack of interest in them and the dearth of servants willing to serve him. Such hideaways never last long by the reckoning of the gods, as Perun has a habit of flattening them when he happens to notice them, but even so some have endured for centuries before crumbling into the ground from neglect.
        Aside from his formidable magical powers and renowned bad attitude, Koschei is most famous for the veracity of his epithet, the Deathless: he cannot be killed by any means. Weapons may injure him but never render him unconscious or at death’s doorstep; starvation and lack of sleep can weaken and disorient him, but he never fully succumbs to them. The only way to successfully destroy Koschei is to locate his soul, cunningly hidden on the isle of Buyan, and damage it irreparably. Koschei’s soul takes the form of a small egg, about the size of a robin’s; this egg is inside a large duck, which in turn is miraculously inside a swift hare, which is kept in locked chest buried beneath a wizened, scraggly tree in the center of the island. Capturing the soul requires first a Dexterity + Larceny roll of at least 25 successes to open its lock, or a Strength + Athletics roll of the same to break it. Once it has been opened, a Dexterity + Brawl roll that gains at least 30 successes is needed to catch the swiftly-fleeing hare, and as soon as it dies, the would-be conqueror must roll Dexterity + Brawl again and gain 35 successes to catch the fleeing duck that springs from its corpse (those without the Wind’s Freedom boon or the Holy Bound knack may also find it difficult to catch the duck, which instantly leaves the ground in its attempts to escape). Upon killing the duck, the egg housing Koschei’s soul is finally free; anyone who destroys it by physically striking Koschei with it will finally cause him to meet his demise. It is possible to break the egg without employing it against Koschei, but doing so requires a 50 on a Strength + Brawl roll, and merely incapacitates Koschei for one day before his soul returns to him and he is free to hide it once more.
        Koschei has a Legend rating of 7.
        Attributes: Strength 6, Dexterity 5, Stamina 7; Charisma 1, Manipulation 5, Appearance 6; Perception 4, Intelligence 4, Wits 6
        Virtues: Ambition 4, Conviction 3, Endurance 5, Piety 1
        Abilities: Academics 1, Animal Ken 1, Athletics 3, Awareness, 2, Brawl 4, Command 3, Control (Horse) 3, Fortitude 5, Integrity 2, Larceny 5, Melee 2, Presence 4, Stealth 2, Survival 3
        Supernatural Powers:
        Boons: Koschei has all boons 1-6 in the Chaos and Magic purviews.
        Epic Attributes: Epic Strength 6, Epic Dexterity 4, Epic Stamina 6; Epic Manipulation 3, Epic Appearance 5; Epic Perception 3, Epic Intelligence 3, Epic Wits 6
        Other: Koschei can never be incapacitated, knocked out or killed by any means except for the destruction of his soul; no matter how heinous the injury or total the devastation of his body, he will slowly regenerate and rise again despite all attempts to end him.