Hydreigon is a three-headed, draconic Pokémon with six thin, black wings that each end in two points on its back. Its body is primarily dark blue, with black fur covering its necks and shoulders. The inner fur surrounding its heads is fuchsia in color, and resembles collars. Hydreigon's heads have black eyes; the main head additionally has fuchsia pupils and visible pointed teeth, while the secondary head's eyes are simplistic and unable to blink. Its abdomen has two fuchsia stripes and its feet appear atrophied, having no claws or defined soles. 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. However, the anime has depicted Hydreigon as being fairly obedient when around its Trainer. The three heads take turns when attacking, not stopping until their target is defeated. Hydreigon can also use its three mouths to rapidly eat through anything. Despite its three heads, it is a singular entity, unlike its pre-evolved form Zweilous; its secondary heads lack brains and do not move or think of their own accord. Conversely, with its central head housing its brain, Hydreigon is said to be highly intelligent in spite of its constantly destructive thoughts. Hydreigon lives high up in the air and has been known to ambush opponents from above. Many stories described Hydreigon destroying entire villages. However, Hydreigon is afraid of Noivern during nighttime. It is said Hydreigon's reason for being ferocious is due to ancient people loathing it. The ancient people believed Hydreigon was evil incarnate, hence always attacking it.
Iron Jugulis shares a resemblance to Hydreigon. The reason is believed due to it being a possibly futuristic hybrid made from combining Hydreigon and machines together as one. It is also rumoured that Iron Jugulis is the child of a Hydreigon which fell in love with a machine.
In JN146, a Hydreigon appeared under the ownership of a Pokémon hunter who was attempting to capture Latias and Latios. The two Pokémon were rescued by Ash, who teamed up with Latios to defeat the hunter.
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 evolves from its pre-evolved form starting at the highest level of all Pokémon that evolve by leveling up, at level 64.
According to interviews with Ken Sugimori in Nintendo Dream, Hydreigon and its evolutionary family were originally intended to have aspects of tanks. These Pokémon were scrapped until late in development, when they were revived and remade to be based on Yamata no Orochi.
Hydreigon shares its category with Sharpedo. They are both known as the Brutal Pokémon.
Hydreigon is based on Yamata no Orochi, a red-eyed, eight-headed dragon or serpent from Japanese mythology. However, compared to Yamata no Orochi, Hydreigon was designed with fewer heads to appear less off-putting, although its wings were designed as a nod to the Orochi's additional heads. Its three heads and Shiny coloration also resemble the Zmei Gorynych, a cunning and deceptive dragon or serpent in Slavic folklore with green scales and a head count of three or its multiples. The tank tread-like markings on Hydreigon's body appears to be a remnant of when Hydreigon's evolutionary line were originally designed after tanks.
Hydreigon may also incorporate elements from other many-headed antagonistic dragons or serpents in various mythologies, such as the Lernaean Hydra, Zahhak, or the Yelbeghen.
Hydreigon may be a combination of hydra, drei (German for three), and dragon.
Sazandora may be a combination of 三 san (three), 残忍 zannin (brutal) or 残酷 zankoku (cruel), and dragon or hydra.
In other languages
From 三 sa / san, 残忍 zannin or 残酷 zankoku, and dragon or hydra