Hoopa did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Wait 3 days after using Prison Bottle Put Hoopa in a PC Box
Hoopa is a Psychic/Ghost-typePokémon, and is considered the second of three Mythical Pokémon in Kalos. Hoopa has control over rings that are able to bend dimensions at will, and move objects of varying sizes from and towards great distances. It's theorized that the mysterious holes found on some of the Mirage Spots in Hoenn are created by Hoopa.
Hoopa has two formes: its first one, Hoopa Confined, is its regular, quite tiny forme. Its second forme, Hoopa Unbound, can be seen as its true forme, and can be unlocked by using a Prison Bottle on Hoopa. Hoopa Unbound is much larger than Hoopa, and its typing has become Psychic/Dark. Hoopa Unbound will revert to its Confined form after three days, or after it's being stored in a PC Box.
Hoopa Confined has a lilac-grayish body. It has pink hair with a ponytail, and several markings of this same color, including a V-shaped one on its torso. There's also a yellow, oval marking on its forehead. Its eyes have yellow sclera, green irises and white pupils, and its eyes are directly connected to its light pink round cheeks. It has a mischievous grin on its face. On each side of its head is also a dark gray, curved horns, each with a pink rim. Hanging on each horn is a golden ring, which Hoopa can use its dimensional powers with. A similar golden ring is adorning its waist.Its torso ends with a wisp-like tail as well.
Hoopa Confined's arms aren't connected to its body, but the tips of its arms and shoulders are adorned with a small golden spike, indicating an invisible connection. Its arms lack an upper arm, so it's essentially a forearm with a few segments. Its second arm segments are thicker than the first segments, and have a pink ring-like rim adorned on its wrists. Its hands are triangular, having no fingers other than a thumb.
Hoopa's rings have dimensional powers, allowing it to travel through alternate dimensions and warp space at will. When it discovers something it likes, it usually collects it and pushes it in its ring to stash it in a hidden place only Hoopa can reach. Hoopa is a mischievous Pokémon that just sends about anything and everything it gets to faraway locations.
Hoopa Unbound looks completely different from its Confined Forme, with a more human-like body shape and a more light gray body. The V-shaped marking on its torso has been replaced by a black hole adorned with a golden rim, resembling one of Hoopa's rings. Its hair has grown massively, and its pink chin is now decorated with a beard. Its grin has transformed in a maw with serrated fangs, and close to the corners of its mouth are two long fangs placed on its mandible. Its yellow sclera are now white, its irises are now gold-orange, and its pupils are black. It also gains a beak-like nose, which is also black. There's now a smaller, more circular marking on its forehead as well. Its horns are also more black, less curved and much longer. The pink rim has transformed into pink markings and two golden rings on each side. Two rings are still adorning its horns, but they seem shrunken now. Though, due to Hoopa grown massively, they likely stayed the same size.
Its torso seems to now have six tufts of pink hair, each with a hole inside, as well as six unconnected arms, which seem to fit in well. The arms are now more muscular and unsegmented. The tip of Hoopa's forearms are still adorned, but now with a golden ring and a black spike, which can still be seen when tucked in its body. Its wrists also are adorned with a golden ring. Its hand consists of three fingers: one thumb and two regular ones. Their fingertips end with a black, pointy nail.
Just like the arms and horns, Hoopa Unbound's waist is also adorned with a golden ring, and under the waist are now a pair of legs, and a more lizard-like tail that ends with a pink arrow point. Hoopa's legs have been marked with a pink line with a dot in the middle (which is marked on its knee), and continues until it reaches the central muscles of its feet, which are entirely covered in pink. Hoopa doesn't have any toes, so its feet end with a yellow, curved point instead. Its ankles are yet again adorned with golden rings.
In its Unbound Forme, Hoopa possesses such great power, that it is now able to seize absolutely everything it wants with its six rings and arms. An incident as a result of its greed has Hoopa apparently carrying away an entire castle, just to gain its hidden treasure.
Minimum stats are calculated with 0 EVs, IVs of 0, and a hindering nature, if applicable.
Maximum stats are calculated with 252 EVs, IVs of 31, and a helpful nature, if applicable.
Hoopa is the first Pokémon which Category alters alongside its Forme, unlike many other Pokémon with form differences (which just keep their category name after changing forms). Hoopa Confined is known as the Mischief Pokémon, while Hoopa Unbound is categorized as the Djinn Pokémon.
Hoopa's regular form being an altered Forme and its second form being its true Forme is similar to Giratina's Altered and Origin Formes.
Its method to change Formes, however, is similar to Shaymin's, instead. To change in the second Forme, one has to use a special item on the respective Pokémon, and to revert to the original Forme, the Trainer has to wait for a certain amount of time, or store the Pokémon in a PC Box.
Hoopa Confined's appearance and abilities may derive from common depictions of djinns.
Hoopa Unbound is also inspired by djinns, but also a bit by deities known as Shakti in Hindu belief, which were said to grow multiple arms. Hoopa Unbound may also be inspired by the Gegenees, a race of six-armed giants from Greek mythology. Hoopa Unbound's tail and horns may be inspired by common depictions of demons.