Great thread, thanks.
Two things-
When 'marsh' comes in ('threads his way through yonders marsh') I think it's a corruption of 'mast', i.e. beechmast, that Europeans and settlers would take their domestic pigs to visit in Autumn, for fattening.

Meaning- gives me archtypal shivers.
Ceridwen.
Terry Pratchett's 'Hogfather'

Winter, black branches, snow, blood, death.