Deino is a small quadrupedal reptilian Pokémon that resembles a dragon with slight dinosaur-like traits. It has a ruff of thick black fur covering its neck and most of its head. As a result of the fur covering its head, Deino cannot see. Beneath the fur it has blue skin. It has four short legs, a round blue body, a small ruffly tail, and a spike-like tuft of fur atop its head. It is possible that the pink marks around its collar are wounds, as Deino will tackle things in order to learn about their surroundings, being blind, and are known to constantly injure themselves as a result of their reckless behavior. It will also bite and eat anything.
This Pokémon and its evolutions are the first Pokémon with the combination of Dark/Dragon.
Its name, and the names of its evolutions are all based on the German words for one, two, and three: ein, zwei, drei.
The pink spots on the fur around its neck are wounds since it explores its surroundings by biting. This makes it the first Pokémon that its Pokédex image shows it being injured.
Deino is the only Pokémon to have the letters of its English name in alphabetical order.
Deino is based on a young dragon with some traits of a dinosaur. The long black hair covering its face also resembles an emo hairstyle fringe.
Its name appears to be taken from dinosaur and the German word for 'one': ein. It is also possible that Deino's name is derived from that of the prehistoric Deinonychus, a dinosaur which existed during the early Cretaceous Period, or "deinos" meaning "terrible".