A brand new Pokémon has started appearing in Pokémon GO. It was originally spotted in the network data, and then began appearing in the game. When caught, the Pokémon turns into Ditto. Here is a picture of it:
The mystery Pokémon has a metallic-looking body with a hex nut for a head
Niantic, the company that makes Pokémon GO, has suggested this is an intentional reveal and not a mistake.