I suspect that SK has never really inventoried the creatures in his mythos. I loved his description of the portal from another dimension in Crouch End. I'm guessing a similar portal was hidden within the Mist. Unlike The Walking Dead, Drayton (and companions) would not only have to battle the "old ones", they'd have to figure out how to send the creatures back through the portal and also determine how to close the portal. They might even make friends and allies with some of the creatures. Good screen writers could turn The Mist into the best series ever if SK would allow them to categorize his creatures into an organized mythos.