Beaver-people — a fact nobody in the room had understood until Clint turned into one.
The were-castors become concrete this chapter through Clint Smashgrab. He answers the door as a changed creature: the same height but far wider than the already-stocky man he was, covered head to foot in brown, oily-looking fur including over his formerly bald head, with a pair of buck teeth jutting from a rodent mouth that gives him a noticeable lisp, webbed hands, no clothes at all, and a long flat tail that Carl can only describe as a wide black tongue.
Princess Donut delivers the realisation in a whisper — she had not known a castor was actually a beaver, and he is disgusting. Carl admits he had not known either. The name had evidently been floating around as a category without either of them working out what it meant in the flesh.
Clint Smashgrab catches them staring and is unbothered enough to make a joke of it before getting back to the elves shelling the town, which suggests the transformation has cost him nothing in competence.
Squat, immensely broad beaver-folk in dense oily brown fur, with buck teeth that force a lisp, webbed hands, and long flat paddle tails; clothing does not survive the change.
The were-form a townsman of Point Mongo has taken, and a running source of disgust for Princess Donut.