<span>The description of Old Scratch infers he's a demon.... particularly the "great red eyes". The fact that he is "begrimed with soot" alludes to the fires of Hell. Would he frighten me? Defintely.</span>
Right off the bat you can cross out idiom off the list, which leaves us down to slang, jargon and dialect. It isn't very likely it's dialect since that refers more to regional language or a specific group of persons. Now we are down to two possible answers, slang and jargon. Slang is categorized as very informal and is not connected to a particular group or profession. I'm not sure which English you are in but jargon is one of the rhetorical devices learned in AP Language and Literature. To be more specific, jargon IS the language which is involved with a particular group or profession. For example, in terms of running some jargon could be "fartlek" and "strides".
The beggar is bitten by the dog
