There are currently no known written accounts of Slavic mythology predating the fragmentation of the Proto-Slavic people into West, East, and South Slavs, with the possible exception of a short note in Herodotus’ Histories, mentioning a tribe of Neuri in the far north, whose men, Herodotus claims, transform themselves into wolves for several days each year. Some researchers have interpreted this through the Slavic folk belief in werewolves, whilst others believe that Herodotus actually referred to ancient Slavic carnival festivals, when groups of young men roamed the villages in masks, sometimes referred to as vucari (wolf-humans). The identification of "Neuri" with Proto-Slavs remains controversial, however.

Hmm i think it is extreamly possible that Neuri were Slavic and that wolf transformation was some sort of religious carnival. If we look at traditional Croatian Fašnik we can see similar costume to serb vučari you showed. Also Slovene carnival costumes from Goriška look/ed (it survived only in few villages) very similar to serbian vučari as well;



Also i found that in Slovene mythology there is spitrit called Šent. He was also called volčji pastir (wolf shepperd) and he could change others and himself into wolfs. According to legend he rules this world 12 days from christmas on. Also it appears that Slovene sheepherds used to cloth themself in wolf skins not long ago;

[img width=700 height=670]http://www.etno-muzej.si/files/oc/teren_8/8_085.jpg” />