The differences in Kjarl's appearance make me wonder how the Eldritch Extradimensional Entity descending on Mechanicsburg would appear in its own dimension ... or what it would look like when fully in Agatha's.

It would be amusing if the Eldritch Extradimensional Entity turned out to be one of the cast members that we've already met. The Dreen, perhaps? Or even Agatha herself, returning from an adventure in another dimension?