Jim is a great fan of Butcher, and I think Mister is his version of Greebo.
Pratchett describes cats dealing with something by fighting it, eating it, running away from it or having sex with it. Greebo has another option, turn human.
I think when Mister runs out of the traditional cats choices then he turns Malk, making the Changelings choice. Looking at Sarissa born the same time couple of centuries ago with Maeve, a changeling doesn’t age the same way suggesting even though Mister is 18 years old (an extremely good age for a Maine Coon) he doesn’t show it taking down even relatively large Gremlins. Which leads us to another point, he obviously ate the Gremlin and has partaken in the past of the Little Folk, let’s just say you are what you eat, and that ain’t fairy dust in his litter box.
