In its natural form, Ditto is a light-purple or pink amorphous Pokémon resembling a blob. It has vestigial facial features and maintains a fairly consistent appearance in official artwork. This includes two small nubs on its "head," a few soft lumps at its base, and two pseudopod-like protrusions instead of arms. Its face consists of beady eyes and a simple mouth, which is almost always smiling.
Ditto possesses several unique traits that distinguish it from other Pokémon. It can transform into an exact copy of any physical object or living creature, replicating both form and abilities. However, each Ditto has individual strengths and weaknesses when transforming. For example, they cannot maintain their transformed state while laughing, and transformations based on memory might have inaccuracies. The Pocket Monsters Carddass Trading Cards depict Ditto's ability to transform different parts of its body into components from multiple Pokémon simultaneously. In the anime, TCG, and some spin-off games, Ditto sometimes struggles to change its face during transformation—a trait commonly associated with the species despite inconsistencies in core series games.
Although its transformation ability allows Ditto to adapt to nearly anything, it does not get along well with others of its kind, often attempting (unsuccessfully) to transform into them. Ditto can also transform into humans but cannot mimic human speech. To protect itself while sleeping, Ditto transforms into a rock to avoid potential attacks.
(Source: Bulbapedia)
