Nithlings are creatures not created by the Architect, but self-made from uncontained or uncontrolled Nothing. The Nithlings have this autonomy in common with both the Architect and the Old One, but apparently lack the power and creative impulses demonstrated by those elder beings. Some Nithlings appear to have the ability to imitate those they come into contact with. A festering scratch or bite from a Nithling will disolve the victim into Nothing.
There are many different types of Nithlings, as they can easily mutate, however, the known variaties of Nithlings are:
Bibliophages — a snake-like Nithling, expelling a venom that reduces any kind of writing to Nothing. They are attracted to writing, which they then try to destroy.
Fetchers - Resembling hound like men wearing bowler hats (while on earth, the Atlas depicts them wearing clothing akin to a sack), these Nithlings cannot cross thresholds uninvited. They can be banished with salt, which causes them to dissolve, as well as numerous other petty magic. They are forbidden to wear wings or wield weapons, however the ones employed by Monday are issued with wings.
Grannow-Hoinch — a monstrous creature consisting of pure Nothing contained within a silver armature or framework. It resembles a combination of a wild boar and a Unicorn, having a six-foot horn. It is black, and has no visible eyes or mouth. It is extremely aggressive, and will go to great lengths to defeat its opponent. The latest one appears to have been created by Saturday, or one of her superior Denizens.
Spirit-Eater — a creature made by sorceries and a seed item belonging to the person whose physical form it assumes, being designed to imitate them. It requires a year of House Time to grow from Nothing. It can grow mentally conducive mold on people and can only be destroyed if its seed item is plunged into Nothing. The mold originates from the planet called Avraxyn; its mutant form, present in Spirit-Eaters, is transmitted by skin-to-skin contact between and only between the Spirit-Eater and natural beings, wherein after it communicates knowledge of its model to the former. A Spirit-Eater's true form varies and can be seen through a veil of raindrops on a sunny day or by the applicaiton of various sorcery. At all other times, it resembles its model. Its technical name is 'Cocigrue'.
Scoucher — a Nithling originating from small, semi-enclosed spaces. They can take any form, but always has long, sharp, ribbon-like tentacles, with which it causes mortals or Denizens to bleed uncontrollably. It then obtains strength from their blood (or, in some cases, ichor). Silver, ruthenium, rhodium, palladium, osmium, iridium and platinum can kill a Scoucher upon contact.
Feverfew's Cormorants — heralds that communicate to the pirate Feverfew that his treasures have been breached or stolen. Feverfew — Part Nithling, part human, this cruel pirate sails on the Border Sea. He is eventually killed while fighting Lord Arthur.
Gore-Draken — a rare type of Nithling occassionally created when certain lost items come into contact with Nothing, and are hence usually found in the Border Sea, in places where the water impringes on Nothing.Not-Horse — A Near Creation made in the workshops of Grim Tuesday. Not-Horses are red-eyed equines having a metallic skin, three clawed toes on each foot, discerning intelligence, personalities suited for battle, and the ability to march in step with each other. They are used as beasts of burden by the Glorious Army of the Architect, particularly by the division known as the Horde. Other versions of Not-Horses include Winged Not-Horses.
New Nithlings or Newniths — a creature created by the Piper in vast numbers to invade and conquer the Great Maze. The Piper made them as "new Denizens", incorporating as many mortal traits as he could. New Nithlings are much more docile then regular Nithlings. They possess creative impulses and the ability to adapt; without the Piper's leadership, he has said, they would probably prefer to become farmers.
Nightsweeper — a tiny, horse-like Nithling whose sole purpose is to spend one night gathering any contamination that has emanated from the House into the Secondary Realms, with which it then becomes Nothing.
Soot, Grim Tuesday's Eyebrow — One of Tuesday's eyebrows, which was blown from its face when he was experimenting with Nothing. It was blasted into the Pit, where accumulation of Nothing upon it made it strong, mobile, and self-aware. It was able to become stronger by eating the Grims treasures.