In Incarnate Forme, Thundurus is a blue, muscular humanoid Pokémon, which resembles a genie. It is a male-only species with no female counterpart. On its head is a single, long, sharp, purple horn. Thundurus has white, zigzagging, and jutting-styled hair, a spiky white mustache, and two pointed blue ears on either side of its head. Its eyes are yellow with beady white irises and no visible pupils. The front of Thundurus's body is covered in various, irregularly shaped purple spots. Its broad chest consists of two joined diamond-shaped pectorals, its shoulders and elbows are adorned with magatama shapes, and on top of its navel is a teardrop, all colored purple. It has two spotted muscular arms, with five fingers on each hand. Its lower body consists of a trailing cloud, with a thick, long, curling, purple, cable-like tail. Thundurus has six ball-like structures its tail goes through at intervals, like knots in a cord. They are a dark gray color, and each has a long, sharp spike on one side.
In Therian Forme, Thundurus is a large, blue, sleek, bipedal snake or dragon-like Pokémon. The horn on its head is now thicker and extends out more, while its ears become more pointy and pinned back. Thundurus's hair remains the same; the mustache now takes on a more raised snout and fanged-maw-like appearance, with two curving wisps flowing back and past its ears. Its eyes remain yellow, but with larger irises that still lack visible pupils. Its chest remains broad and unchanged, while its navel is bejeweled with a blue gem. Thundurus's arms have lost much of their muscular bulk, and are now slimmer. It has two paw-like hands, each covered in a trailing cloud-like fluff and with three claw-tipped fingers. Thundurus's purple lower half is much smaller than its upper body and consists of two hind legs and its tail. Its feet are elongated, with three downward curved toes and claws. Thundurus's tail also remains largely unchanged, although it is thicker at the base and tapers off, becoming thinner toward the tip.
Thundurus can shoot thunderbolts from its tail. It uses these lightning bolts to annihilate foes into nothingness. It is known to be disliked and feared by people and farmers for its destructive rampages which include fierce thunderstorms. It tends to cause forest fires whenever it flies around shooting lightning. Thundurus's lightning bolts can enrich the soil of any ground it hits. Any area visited by Thundurus is marked by charred remains of areas it destroyed. Thundurus has been known to get into violent conflicts with Tornadus ever since the beginning of time. Thundurus can move so fast it can materialize without warning. Thundurus can unleash mini thunderstorms along with surrounding itself with a cloud shield to protect itself from harm.
Thundurus is the only known Pokémon capable of learning the move Wildbolt Storm.
