Hydreigon is a three-headed, draconic Pokémon with six thin, black wings that each end in two points on its back. It has a fuchsia-colored collar on its neck which surrounds its head. The main head is dark blue and has black eyes with fuchsia pupils. Its two hands are also black and each one harbors a head; these are similarly blue with black eyes with small fuchsia collars on the inside. Its abdomen has two fuchsia stripes and its feet appear atrophied, having no claws or defined soles and two or three small toes. Its tail also sports a fuchsia stripe and ends with a black tuft. Hydreigon is a violent, destructive Pokémon. It will attack anything that moves, determining it a foe. Its heads can consume anything.
NA:Unlike Scizor with its pretend heads, Hydreigon's three heads are real! The center head is the brains of the operation, while the left and right ones are there to consume everything they can. We wouldn't be surprised to see Hydreigon at an eating contest, but there has to be a rule against having three mouths on one body...?
PAL:Unlike Scizor's head-like claws, the heads at the end of Hydreigon's arms are the real deal. Only the head in the middle does any thinking - the other two are just for gobbling up anything in sight. If you think about it, Hydreigon would probably win any eating contest hands down, but... maybe having three mouths is against the rules...
Pokémon Mystery Dungeon: Gates to Infinity: Hydreigon was at first described by Munna as an evil Pokémon who is pure destruction in Pokémon form, devours everything in his path, and said to be the cause of the world's balance being disrupted. In truth, Munna's words about him were all a lie to trick the player, and Hydreigon is really the physical embodiment of the Voice of Life, the form of the world's will to live, who called upon humans to save the Pokémon world as no Pokémon could hope to save it. He originally first contacted the player through a dream before Munna intercepted the vision, and by using Hydreigon's voice, she tricked the player into thinking Hydreigon was evil.
Spoilers end here.
This Pokémon was unavailable prior to Generation V.
Hydreigon is based on the Yamata no Orochi, including its red eyes. Its three heads and Shiny coloration resemble the Zmey Gorynych. It may also incorporate elements of the Lernaean Hydra. These mythological serpents may have inspired Hydreigon's Dark typing, as all three are deadly antagonists, with the Zmey Gorynych in particular shown to be deceptive.
According to interviews with Ken Sugimori in Nintendo Dream, Hydreigon and its evolutionary family were originally intended to be cyborg dragons with aspects of tanks. The Pokémon were scrapped until late in development, when they were revived and remade to be based on Yamata no Orochi. The tank tread-like markings on Hydreigon's body are a remnant of this design. Although Yamata no Orochi typically has eight heads in mythology, Hydreigon was designed with fewer heads to appear less confusing.
Hydreigon may be a combination of hydra, drei (German for three), and dragon. It may also incorporate hydrogen, a gas highly flammable under normal conditions.
Sazandora may be a combination of 三 san (three) and dragon or hydra.
In other languages
Sa and zan are from 三 sa/san, dora is from dragon or hydra