During its development, it was known as Type: Full prior to the project's failure.
Type: Null is a chimeric-looking quadruped Pokémon combining body parts from several different creatures. Its body is black and cat-like, with three-toed paws on its hind legs while its front legs are green and resemble an insect's or bird's. It has purple scales on its upper hips, its tail is a blue forked fin with a grey membrane, and a mane of grey fur hangs around its neck. Its head is mostly obscured by a metallic helmet with a ring resembling that of Arceus around the neck and a silver crest on the top. Its grey eyes are, however, visible through a pair of openings on the helmet.
Along with Cosmog, Type: Null is the first Legendary Pokémon that is able to evolve.
Upon evolving into Silvally, Type: Null's stats remain unchanged except for a slight increase in speed. However, it gains a much bigger movepool and can use a new ability.
The square cuts of hair on Type: Null's mane closely resemble those of Gladion who is Type: Null's trainer.
Type: Null's body resembles that of Umbreon and its tail is reminescent of Gyarados. It also has similar markings on its helmet to Zygarde 10% and a ring on its helmet is similar to Arceus. Its legs are also similar to those of Bug Pokémon, but its feet resemble Grovyle's. Its crest is also similar to the crest feathers of Chatot or the tutu of Oricorio Pa'u Style. Its Normal-type and ability to evolve into a Pokémon that can have many different types is similar to Eevee. Its shady and hidden eyes make it similar to some Ghost-type Pokémon like Dusknoir, Cofagrigus and Phantump.
Along with the Tapu Guardians and Mr. Mime, Type: Null is one of few Pokémon in the series to have a name with two words.
At first, when Type: Null was created, it was called as "Type: Full", meaning that it had the ability to change into different types like Arceus, until the experiment ended in failure.
This also refers that Type: Null is an artificial copy of Arceus.
Type: Null is one of three Pokémon created through scientific experiments by an evil organization, the other two being Mewtwo (created by Team Rocket) and Genesect (created by Team Plasma).
In the anime, Type: Null is often referred to as Silvally. This might be just because Type: Null is simply Silvally with a containment helmet on.
Type: Null has the highest base stat total of all Pokémon that are still able to evolve (534).
Type: Null is the first Pokémon to have its English, Spanish and Italian all be the same.
Type: Null may be based on a gryphon or a chimera. It also has many similarities to the dragon of the Ishtar Gate in the city of Babylon, such as the feline and dragon-like legs, dragon-like shape, and crest on its head. The ring surrounding its helmet resembles the one surrounding the torso of Arceus. It may also draw inspiration from Frankenstein's Monster, especially the bolts on either side of its head.
Type: Null's name is a mixture of type, and null; having no legal or binding force, or the value of Zero. It may also mean "no type" in contrast to "Type: Full" meaning "all types".