If it's Friday it must be Ferrets

I've decided that from now on I shall be employing a fictional ferret grading system (1-5) as follows:-

1 Ferret - the ferret in question is a perfectly normal ferret.

2 Ferrets - the ferret in question is normal but there's something slightly "off" (air quotes) about it. (If it's the first book in the series, the ferret grade may be rising in future books).

3 Ferrets - the ferret in question has some supernatural attributes but they are not annoying and contribute in a useful way to the story.

4 Ferrets - the ferret in question is obviously supernatural. And its talents are more annoying than useful (though it does have its cute moments). It doesn't save the day but without its contribution the hero/heroine would have hit a brick wall.

5 Ferrets - the ferret in question is actually a disguised prince/magician/genie, travelling under a curse/spell. Without him the heroine would never have solved the problem / won the war. It puts the ferret in ferret ex machina.