The form of Dudunsparce it evolves into — either Two-Segment Form or Three-Segment Form — depends on its encryption constant. Since this value cannot be influenced or seen by the player, what a given Dunsparce will evolve into is essentially random — with a 1/100 chance of evolving into Three-Segment Form Dudunsparce.
Dunsparce is a serpentine, and somewhat insectoid, Pokémon with a primarily yellow body, blue underside, and blue-and-cream-striped back. Its head is round with a wide mouth extending under its jowls and curving up toward the middle of its face. Its chin is blue with two rounded prongs. Its eyes—round and rimmed with blue—are kept closed, revealing its cream-colored eyelids. On Dunsparce's upper back are two tiny white wings. Its body ends in a drill-like tail.
Dunsparce can float slightly with its wings, which some scientists believe were used to fly in the sky during ancient times. However, it avoids detection and flees when spotted by burrowing into the ground with its tail. It lives immobile in caves and beneath the earth, where it makes maze-like nests. They get along with Diglett and share tunnels with each other. Dunsparce can navigate through its nests without getting lost by the smell of the dirt.
Dunsparce appears to be based on the snake-like Tsuchinoko cryptid of Japan. Visually, its design may be a pun on one of the cryptid's other names, バチヘビ bachi hebi (bee snake), as Dunsparce appears to combine bee- and snake-like features. It may draw specific inspiration from digger bees. Dunsparce may also have connections to Amphipteres, such as Quetzalcoatl, or flying snakes.
Given its larviform appearance, horn-like tail, and ring-circled eyes that resemble the eyespots of some species, Dunsparce may draw inspiration from sphinx moth caterpillars, which have a history of being mistaken for the Tsuchinoko. Its closed eyes likely reference the ocular vestigiality demonstrated by many subterranean animals, though they may also nod to the Nozuchi, a creature thought to be synonymous with the Tsuchinoko that is sometimes depicted as a giant, eyeless caterpillar.
Dunsparce may be a combination of dun (subadult mayfly; or dark/gloomy, referring to its preferred habitat) or dunce and sparse.
Nokocchi may be derived from an anagram of ツチノコ, the katakana spelling of 槌の子 tsuchinoko (a fabled snake-like creature).