While it is not known to evolve into or from any other Pokémon, it has an alternate form, which it changes into by using the Prison Bottle. Its default form, Hoopa Confined, will then become the Psychic/DarkHoopa Unbound. Hoopa Unbound in the party will revert into Hoopa Confined if three days have passed since changing to Hoopa Unbound. Other circumstances may also cause it to revert.
Hoopa Confined was officially revealed in the February 2015 issue of CoroCoro magazine. Hoopa Unbound was officially revealed in the May 2015 issue of CoroCoro magazine.
Hoopa Confined is a light purple Pokémon with several pink markings. There is a v-shaped marking on its chest and bands around its wrists. Additionally, there are pink markings around its head and a growth on top resembling hair tied into a ponytail. There is a yellow, ring-shaped marking in the center of its forehead, and it has green eyes with yellow sclera. On either side of its head is a dark gray horn that curves slightly upward. Hoopa has three gold rings: one large one around its lower body and one hanging freely on each of its horns. Its arms are not attached to its body and float next to it. Each arm has a small golden spike on one end and a hand similar to a mitten on the other. There is a golden spike on each shoulder, which is similar to those on its arms. Hoopa's lower body consists only of a wispy structure similar to its ponytail.
Hoopa Unbound has a similar color scheme to Hoopa Confined, although the main color is now a light blue and its markings are slightly darker. This form is bipedal and has six arms. The ponytail on its head is larger and bushier, and its eyes are now yellow with white sclera. Its horns are darker and less curved with spiky, purple fur at their bases. This form has a pointed, dark gray snout and a mouth full of pointed teeth. Several tufts of purple fur surround its torso. Each of its arms is disconnected from the body and has a gold ring on one end and a three-fingered hand on the other. It has a ring around each wrist as well. Many other rings are present on this form: there are two around each ankle, two around the base of its ponytail, two at the base of each horn, one near the center of each horn, one around its waist, and one encircles a black hole in the middle of its body. The circular mark on its forehead also surrounds a much smaller black hole. A purple, protruding stripe extends down each leg, widens at the knee, and makes a circle around the tip of the foot. Additionally, this form has a tail with a purple stripe along the top and an arrow-shaped tip.
Hoopa has the power to transport things using teleportation, which warps space. Hoopa Unbound is said to be Hoopa's true form. Hoopa Unbound is said to have the power to bend dimensions which allows it to seize anything in the world. As seen in the anime, Hoopa Confined and Unbound can travel through their rings and Hoopa Unbound has the ability to control and summon powerful Legendary Pokémon. Hoopa Confined is the only known Pokémon that can learn Hyperspace Hole. Hoopa's alternate form, Hoopa Unbound, has its own signature move, Hyperspace Fury.
Hoopa Confined may have been inspired by common depictions of djinn, particularly those with wisp-like tails. Its having rings around its wrists could have been inspired by the djinn in the story of Aladdin.
Hoopa Unbound may also have been inspired by djinn, while its six arms may be drawn from the Hindu deities known as Shakti, who were rumored to grow multiple arms. It may also be based on the Gegenees, who were a tribe of six-armed giants who fought the Argonauts in Greek mythology. Its tail and horns may also derive from common depictions of demons.
Both forms of Hoopa could also be partly based on the legend of Nezha, a deity worshipped in Taoism and Chinese folk religion and commonly referred to as a trickster deity and a worldly protector. Very much like Hoopa Unbound, Nezha is depicted holding rings and is sometimes depicted with multiple arms. Its ability to use its hoops to transport things may be based on portals.
Its relationship with the Prison Bottle is similar to the djinn's with its lamp in traditional Arabian stories, since its full power is sealed within its respective vessel. Hoopa's only being able to maintain its Unbound state for three days parallels the limit to the number of wishes a djinni can grant to its current master. In both Formes, its Shiny coloration reflects on the Arabian origins of djinn.
Hoopa is derived from hoop. It may also be derived from hoopla (something loud, attention-grabbing, and possibly misleading).