If somehow you have no idea what is in our fanart Pokémon Ditto Muscles Sticker - it's not a stain. It is a Normal-type Pokémon introduced in Generation I, which is not known to evolve into or from any other Pokémon. This unusual Pokemon is well-known for its unique ability to breed with any Pokémon other than the Pokémon in the No Eggs Discovered group and other Ditto, including some gender-unknown Pokémon, to produce Eggs of the other's species.