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's 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's 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's 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's 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's 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 (320 kilometers per hour). It can also whip up storms with its tail, and is able to blow away houses.
A Therian Forme Tornadus appeared in the Hoopa's Surprise Ring Adventures short Flying in the Air. He was among the immense Flying-type Pokémon summoned by Hoopa to create wind for Ash and Pikachu, but their combined Gust was too much for them and sent them blasting off.
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.