the founder and true leader of the balle masque, The snake of the festival, who at this point is only know as the Silver, was sealed within the reiji maigo because of sabrac´s actions and he eventually ends up merging with Yuji and lending him his power, and his black flames. The silver flames thingy is a bit more complicated. The snake of the festival is actually one of the true gods of the crimson realm along with alastor and is the Sozoshin( god of creation). Unless i´m mistaken, the silver flames were a byproduct when he created the siver knight( the one who the arm belongs to) to use it as a puppet body. really confusing.