Jenny Green-Teeth is the first wave of the Queen of Fairyland's attack against Tiffany Aching. She has long skinny arms that emerged from the water and clawed at the place where Tiffany had been, a thin face with long sharp teeth, huge round eyes, and dripping green hair like waterweed. Tiffany knows her from a picture in one of the few books in the house, The Goode Childe's Booke of Faerie Tales.
Being of an enquiring mind, she wants to know what the book means by "eyes the size of soup plates", and measures some from the dresser. Eight inches, actually. Being the kind of person who runs towards things rather than away from them, she takes the largest frying pan from the kitchen, and using her small brother as bait, lures the creature out of the stream again, and deals with it with the frying pan. Jenny may have been at a disadvantage, possibly bewildered at being in a stream when her natural habitat is stagnent water, but the fact that the frying pan was made of iron was decisive.
Tiffany's wish to know more about Jenny Green-Teeth leads her to Miss Tick. Jenny Green-Teeth is woven from her own imagination as much as anything else, but all the monsters are coming back, even the ones out of books. It is, as Miss Tick says, the start of a major incursion. There is nothing standing in the way of it except Tiffany. The last thing the old Kelda says to her, before she seeks to enter Fairyland to rescue her brother, is "Somewhere, a[ll] stories are real, all songs are true..." Miss Tick says something very similar, so it must be important.
Miss Tick describes Jenny Green-Teeth as "only a Grade One Prohibitory Monster". This refers to a schema which appears to be of Miss Tick's devising, and which she may have set out in a book called the Bestiary of Transient Monsters. The schema is summarised on a sample diary page provided in The Illustrated Wee Free Men.
- Grade 1: monsters invented by adults to scare children from dangerous of forbidden places (prohibitory) - Jenny is an example given, among others.
- Grade 2: monsters invented by adults to scare anyone, anywhere. One of the examples is The Headless Horseman.
- Grade 3: monsters by accident (mostly). e.g. The Eater of Socks.
- Grade 4: monsters here for purposes of their own (such as the Hiver).
- Suggested new Grade 5: monsters invented by children for children!!! The worst kind!!! Two examples from those given being The Child-eating Puddle, and The Snot Fairy (a type of Bogeyman).