There is no suggestion in English forms that the Knight has supernatural powers. I'd need to check but I'm not even sure that many, if any, of the continental versions do. This seems to be a later addition as with other cases of the Scottish redaction adding in the supernatural elements.

Have we identified 'EMUN'? This astounding revelation 'I have by me a copy, in black letter, of the OK.' If that can be verified that would just about settle the case. Having said that the likelihood of a black-letter version being around then and no recollection of it surviving makes me suspicious. The earliest we have is 1780, yes?

Once again, ballads, like their close relatives folk tales, do not need to be plausible. Describers of ballad style often refer to their cartoon-like qualities.