Hairball Monsters are little piles of Troll hair that have come to life. The ones seen in the series are entirely black with red eyes and sharp fangs. They move about by either jumping, crawling or rolling around.
Hairball Monsters have the ability to multiply as many times as they want instantly. They are extremely aggressive and vicious and will attack anything or anyone that comes close to them. They are quite resilient, but can be defeated easily if hit hard enough.
- In order to defeat the Hairball Monsters, Jake and Stan Lipkowski, the Troll from which they came from, sucked them into a vacuum cleaner which they threw out the window.
- Hairball Monsters look somewhat similar to Fizzgig, a fuzz ball dog-like pet featured in The Dark Crystal movie.