Hydreigon is a new pokemon in Pokemon Black and White. Hydreigon is a Dark/Dragon type and can not be caught in the wild. Hydreigon evolves from a Zweilous at level 64, which evolves from a Deino at level 50.
Deino is the only pokemon in the evolution chain that can be caught in the wild, so you’ll need to catch it to get Hydreigon.
Hydreigon is a powerful pokemon with a lot of attack, and stats that nearly match some of the legendaries in the game.
