Hmmm.... That is a polish I think, maybe it's a deformity?? Polish are supposed to have 4 toes like other chickens do. So I dunno why it has extra toes. Either way, it shouldn't hurt it in any way.
I'm thinking that little guy might be a mottled Houdan, which have five toes. If it is a Houdan, it'll look spotted instead of laced like a Polish would.