Regidrago is a spherical, golem-like Pokémon. It has a dark red body made of crystallized dragon energy, with the energy being the densest at its central core. Its face has a pattern of seven blue dots that resembles the capital letter "Y". It has two red legs with black feet that are shaped like teeth. Its arms are black on the outside and dark red on the inside, and resemble a dragon's head; the right arm resembles a dragon's upper jaw, complete with horns and "eye sockets", while the left arm is shaped like a lower jaw. Two red spikes shaped like wings are located behind its back, although it doesn't use these to fly, as it is capable of floating in the air. Regidrago's body and the "eye sockets" on its right arm can glow pink when attacking.
According to legend, Regidrago was created by Regigigas using crystallized dragon energy; however, Regigigas ran out of crystals after building Regidrago's head. Regidrago was then sealed away in a temple by ancient people, who feared the destruction it would cause should it ever be completed. Due to its body composition, Regidrago is said to have the most powerful Dragon-type moves of all Pokémon, along with the power of every Dragon-type Pokémon.
Regidrago can fire an attack made of intense dragon energy by combining its arms to form a mouth, as seen with its signature move, Dragon Energy. There is an unproven academic theory that posits that Regidrago's arms originated from the head of an ancient dragon Pokémon.
Regidrago's base HP and Speed stats are the reverse of Regieleki's.
Regidrago is the only pure Dragon-type Legendary Pokémon.
Regidrago seems to be based on the golems of Hebrew legend. The legends cast them as servants of higher powers and are said to have writing on their heads. When the writing is removed, the creature would be weakened, or even killed in some legends. Regidrago's face that consists of seven dots may be based on Braille alphabet which was necessary to use to encounter the Legendary giants for the first time in Sealed Chamber.
Regidrago also seems to be based on a dragon head and a crystal ball or a pearl held by an Asian dragon.
The five Legendary giants may collectively be themed after historical epochs, with Regidrago representing the Middle Ages, a period known for its legends of dragons. Alternatively, Regidrago may represent the Mesozoic, the era when dinosaurs walked the Earth which is also known as the Age of Reptiles. Regidrago's being the remnants of an ancient dragon or crystalized dragon energy may be a vague reference to fossil fuels.
Regidrago and Regidorago may be a combination of regis (Latin for royal) and dragon.