Tornadus 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):
In Incarnate Forme, Tornadus is a green, muscular humanoid Pokémon, which resembles a genie. It is a male-only species with no female counterpart. On its forehead are two, purple, long and sharp horns. Tornadus has white, wavy and billowy styled hair, a spiky white mustache and two pointed green ears on either side of its head. Its eyes are yellow with beady white irises and no visible pupils. The front of Tornadus' body is covered in various, irregularly shaped purple spots. Its broad, purple chest consists of two joined, partially diamond shaped pectorals and its shoulders, elbows and navel are adorned with raindrop like designs. It has two spotted muscular arms, with five fingers on each hand. Its lower body consists of a trailing cloud, with a purple long, curling tail, tipped with a whirl. Spanning the length of its tail, Tornadus has several whorled structures. They are a light Khaki color, and follow the same direction as the tip of its tail.
In Therian Forme, Tornadus is a large, green, bipedal, long-necked, bird-like Pokémon. It now lacks any visible ears, and the horns on its forehead have become thinner and crest-like. Tornadus' hair is also now crest-like, and the direction of its hair whirl is reversed. The style of its hair is now more relaxed as well, proudly flowing down its long neck. Tornadus' mustache now takes on a more beak-like appearance, puffing out on the edges like coarse plumage against its cheeks. Its eyes remain yellow, but with larger irises which still lack visible pupils. Its chest is now fuller, but remains largely unchanged, while its navel is now bejeweled with a red gem. Tornadus' arms have now become large spanning, feathered wings; each possessing thumbs and five large, purple tipped primary feathers. It has two strong legs and sharp talons, each with three sharp purple claws and one dewclaw. Tornadus' tail remains largely unchanged, although it appears slightly longer and less curved than before. On its lower back, it has a large trailing cloud-like puff.
Tornadus can travel at speeds of 200 miles per hour (300 kilometers per hour). It can also whip up storms with its tail, and is able to blow away houses.
Tornadus is the only pure Flying-type Pokémon. However, other Pokémon are able to temporarily become pure Flying types through their Abilities or moves, such as Kecleon and Arceus.
This also makes it the only single-type Pokémon with a unique type combination.
Tornadus and Thundurus have identical base stat distribution in their Incarnate Formes.
Tornadus is the only single-type Legendary Pokémon introduced in Generation V.
When Tornadus appears on Route 7 in Pokémon Black, Thundurus's cry is heard.
In an interview with Nintendo Dream, Ken Sugimori revealed that Tornadus was originally intended to be red.
Prior to Generation VI, Tornadus's Therian Forme had the same body style as its Incarnate Forme.
In Incarnate Forme, Tornadus is based on Fūjin, the kami of wind. It may also have drawn inspiration from genies.
In Therian Forme, Tornadus seems to be based on a bird of prey, most likely an eagle, vulture or other large avian species. It may also draw inspiration from the Vermilion Bird of the Chinese Four Symbols constellation, or from Huitzilopochtli, a god from the Aztec mythology that resembles a hummingbird.
Tornadus and Tornelos may be derived from tornado and Aeolus, ruler of the winds in Greek mythology.