Яга
Vermeer W. Why Baba-Yaga? Substratal phonetics and restoration of velars subject to the Progressive Palatalization in Russian/Belorussian and adjacent areas (appr. 600-900 CE) // A Linguistic Map of Prehistoric Northern Europe (Mémoires de la Société Finno-Ougrienne 266). Helsinki, 2012 , c. 345-370
фольклор
"Russian stem-final -g- corresponds with the reflex of PSl *-dź- found elsewhere in Slavic, e.g. Polish jędza ‘witch’. Here PSl *-dź- reflects early Slavic *g as modified by what is known as the Progressive Palatalization"
с. 345
этимология