Hydreigon is one of my favourite Dragon and Dark Pokemon ever!

Hydreigon (Japanese: サザンドラ Sazandora) is a dual-type Dark/Dragon pseudo-legendary Pokémon introduced in Generation V.

It evolves from Zweilous starting at level 64. It is the final form of Deino.

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 colour 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. Noivern is the natural enemy of Hydreigon depending on the time of day despite Hydreigon being afraid of it. 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.