Deino is a small blue skinned quadrupedal Pokémon with black fur covering its head and neck which conceals everything but its mouth from view. The fur around its neck also has six purple spots encircling it, which resemble bruises. The hair on the top of its head takes the shape of a single small horn. It also has a short tail.
Deino have the vigor and energy to bite constantly and without stopping.
Because they are blind, Deino will bite at anything. They never stop biting, and are therefore dangerous to approach without taking precautions. They will also ram anything, ensuring that they always have bruises all over them.
As seen in The Lonely Deino, Deino may rear up on their hind legs when they are happy.
Deino primarily lives in caves with abundant water sources.
Three Deino made their debut in The Lonely Deino! under the care of a Day Care owner named Bobby who was looking after them for their Trainers. Two of the Deino were very rambunctious while one of them was shy and refused to eat. Iris tried to use her experience with Dragon-types to help it feel more comfortable around strangers.
Deino is the only Pokémon to have the letters of its English name in alphabetical order.
According to interviews with Sugimori in Nintendo Dream, Deino and its evolutions were originally intended to be cyborg dragons - part tank and part dragon. They were then scrapped until late in the game when they were revived and re-made to be based on Yamata no Orochi.
Deino may be a combination of dino (informal name for dinosaur) and ein (German for a, and part of the German for one, eins). It may also derive from δεινός deinos (Ancient Greek for terrible). It may also refer to dinosaurs such as the Deinosuchus and Deinonychus. Deino was also the name of one of the Graeae who, in Greek mythology, were three sisters who only had one eye between them, meaning that while one had the eye, the other two would be blind.
Monozu may be a combination of mono (prefix meaning one) and 頭 zu (head). Its full name literally means "one head".