What is yallery brown?

Yallery Brown is a character from a children's book by Brian Jacques called "The Ribbajack and Other Curious Yarns." He is described as a mischievous and sometimes troublesome fairy who lives in the woods. According to the story, he enjoys leading people astray and causing chaos, but he can also be helpful and playful at times. The character of Yallery Brown is often used in folk tales and legends as a symbol of trickery and mischief.