A while back I saw a theory based off a WoJ that talked about Demonreach and how it can release only certain parts of it's prisoners. The theory explained how this could be used to remove the influence of Nemesis
We know walkers can take a quasi-physical form, as we saw when Harry went against HHWB
But I don't think [Spoilers ahead] HHWBeside has shown a physical form
My idea is that what if HHWBeside can't exist outside of the Outside, hence why they possess people (as well as gaining powerful vessels/influence)
But, assuming this was correct, what would happen if Harry caught, for say, Justine, and separated the Walker from her - and released the Walker without a vessel, under his influence (Starborn, theoretical)