Decidueye is a tall, avian Pokémon that resembles an owl. The upper portion of its face is dark green with a thin, orange mask-like marking encircling its eyes. Its eyes are reddish-orange and it has a hooked dark green beak. The feathers covering its wings and back are brown, while the rest of its body is primarily white. The three feathers at the tip of each wing are structured similar to fingers and have lighter tips. The backs of its wings and torso are dotted with many white spots, there are six on each wing. The inside of each wing has a line of upside-down, reddish-orange triangles across the top. It has long legs, feet with two toes facing forward and two backward, and short dark green talons. Its tail consists of three long, green leaves.
A leafy hood covers its head and shoulders, and partially covers its face. The hood is smoothly draped across the shoulders and back, but has uneven edges. Around the head, the hood forms many pointed projections that extend over its face. A single white feather with a reddish-orange base extends from the top of its hood. In the center of its chest is a reddish-orange X shape formed by dead leaves with two thin green vines extending from it. Pulling on the vines closes the hood further over Decidueye's face and improves its focus.
While this Pokémon is cool and cautious by nature, it begins to panic if surprised. It can hide from opponents by masking its presence, allowing it to attack unaware foes. It takes only a tenth of a second for it to pluck, aim, and fire an arrow quill from its wings. It is not only quick but also accurate, capable of striking targets over half a mile away. Decidueye is the only known Pokémon capable of learning the move Spirit Shackle and the corresponding Z-Move Sinister Arrow Raid.
Compared to Alolan Decidueye, Hisuian Decidueye has a smaller wing area and thicker legs. The plumes around its ankles are longer, its feet are black with white talons, and its tail feathers are red. Its head and neck covering are also red, with orange and white accents, and together they resemble an ayaigasa. Its wings appear to have more layers, and the rachises of its feathers are capable of storing air, allowing it to withstand the extreme cold of the Hisui region.
Hisuian Decidueye is said to have a stalwart, fierce personality, although it will tolerate those who do not act hostile towards it. Unlike its Alolan counterpart, it prefers to fight at close-range in order to overwhelm enemies. It tends to have a nomadic lifestyle, wandering the region in search of food. Its legs can deliver powerful kicks that can knock down trees and destroy boulders. Hisuian Decidueye's signature strategy for attacking its foes is to fly forward to unleash kicks, then use its hidden arrow quills in order to deliver multiple attacks in a row. This can be seen in its signature move, Triple Arrows.
- Official confidential art featuring Decidueye, Incineroar, Primarina, and Mallow was leaked on the Internet on June 4, 2016. This leak happened 145 days before these Pokémon were officially revealed on October 27, 2016. From the leaked material it is known that Decidueye's code name was "フクロウ 3", or "Owl 3" during development.
- Decidueye was originally considered for Super Smash Bros. Ultimate, but director Masahiro Sakurai decided to go with Incineroar instead.
- Decidueye is the only non-Mega-Evolved starter Pokémon that has its secondary type changed.
- Decidueye and its pre-evolutions:
- Decidueye is the only Pokémon introduced in Generation VII to have a regional form.
- Of all Pokémon that have received a regional form, Decidueye's regional form was introduced in the shortest time after the species's introduction, being introduced just one generation later.
Decidueye is based on an owl. It is most similar to the pueo owl in particular, which is a common physical form of the aumakua, ancestral spirits in Hawaiian culture. This may account for its Ghost typing. Additionally, it has some traits similar to the common barn owl – which in some territories is also known as the "ghost owl" – and the extinct stilt-owl. In general, an association between the supernatural and owls was once a very common motif, as they were seen as both bearers of death and disturbed spirits throughout history. Decidueye also shares elements with an archer and common depictions of the English folk hero Robin Hood.
Hisuian Decidueye's earthy coloring and comparatively shorter wings seem to draw inspiration from the color change deciduous tree leaves experience during autumn, signifying its growth. Its hat-like crown of feathers resembles a kasa, or traditional Japanese brimmed hats, perhaps the ayaigasa specifically worn by samurai archers for hunting or ceremonial purposes. Additionally, the motif of autumn leaves is commonly associated with Rōnin, samurai members who have fallen from grace and usually have been ousted. This is also suggested by its wandering lifestyle. It may also be inspired by Cikap-kamuy, the Ainu god of owls and the land; and hence inspired by Blakiston's fish owl. It also shares similarities with primarily ground-dwelling burrowing owls and secretarybirds. Hisuian Decidueye's Shiny coloration is similar to Alolan Decidueye's normal coloration.
Decidueye may be a combination of deciduous, duel, and deadeye or bullseye.
Junaiper may be a combination of 樹 ju (tree), juniper, and sniper.