Vyedun and Vyedma are both 100% Russian words. Maybe Finnish too, I dont know. For Vyedun, literally 'Knower', I cant think of an exact analogue, its somethink like 'one who's got arcane knowledge', and Vyedma is 'Witch'. Well, maybe not exactly the type of witch Marignon hunters are looking for, but its an exact translation. Baba Yaga is an archetypical 'Vyedma'.
'Rus led by Vanir' was my first thought when I've read this word on this forum too, of course. Vikings, also called 'varyags' in Russia (supposedly derieved from norse vaeringjar), were indeed a major part of life in Rus as traders, druzhina warriors or boyars (nobility). Surely, Vanir would have an even greater influence.
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By the way - do Firebirds bring good luck indeed, or is it just a superstition?
I mean, is it worth summoning a few in my cities just to fend of misfortune, or not?