Sounds like the other commenter got it. I’m commenting because the only time I’ve ever posted about a book o couldn’t remember was “The Dark Lord of Derkholm” also by Diana Wynn Jones! Great book of you haven’t read it. She wrote Howell’s Moving Castle too.
Pamphilius: https://www.inaturalist.org/taxa/495068-Pamphilius?locale=en-us