Native to the Mire and the Undertown sewers, Muglumps are a hideous race of amphibious, predatory animals. Physically resembling a vicious prowlgrin, they may be related to prowlgrins, yet are predators. Muglumps slide through mud and they have poisonous sycthes for feet. They are tame in the sewers, their nature reduced by difficult environments. But in their home in the Mire, they are ruthless and fast.
Muglumps are mentioned in book six of The Edge Chronicles as being fearsome creatures which are intelligent enough to manipulate objects and make traps such as hanging nets for their victims. Muglumps are rarely seen in the Undertown sewers but do live there. They are thought to be an urban legend.
Later on in book seven, the Muglumps first make their appearence. One Muglump attacks Rook Barkwater and Felix Lodd on their way to the Knighting Ceremony. This Muglump can distort itself and hang from ceilings, walk on walls, and outmanouever the most skilled fighters. The Muglump survives the attack, ruthlessly brushing Rook aside and running down the sewers.
In the Exodus in book nine, the Muglumps are one of the dangers facing the Undertowners on their voyage. The Muglumps are encountered en masse on the Mire, and devour the prowlgrins before attacking the Undertowners. But the townspeople escape thanks to the ghosts of Screetown, outcasts and rebels who can fight monsters. The ghosts fight the Muglumps and drive them back at great loss to the Library carts.