Peppercorn is the pet-nitten of Alfur Aldric. She lives with him in his house within Hilda's house, and is first seen in "Chapter 12: The Replacement". She is only a minor character in that episode.
While it is not stated in the series itself, she is most likely one of the nittens that Angelina gave birth to in Hilda's hair in "Chapter 1: The Hidden People". She has the same mousey brown fur as Angelina and her young. What sets her apart from them is the fact that her paws, the tip of her tail, and a patch of fur around her right eye are a different color.
While Alfur loves her, Alvin did not when he came to replace Alfur as the Trolberg Correspondent.