Ditto

Ditto (Japanese: メタモン Metamon) is a -type Pokémon introduced in Generation I. Ditto are unique, as their only attack is Transform. They use this attack to copy the stats (except HP), moves (only 5 PP), types, and the appearance of the opponent. Another reason that they are unique is that Ditto can breed with any Pokémon in a Day Care Center regardless of its gender, except other Ditto and legendaries.

Appearance
Ditto's appearance is very plain. It is a simple pinkish purple, amorphous blob, with two smalls dots as eyes and a long, curved mouth. Though it's appearance can be changed via Transform. A shiny Ditto is blue as opposed to the normal purple. Ditto's cry is also known to be the same as Poliwag's in the game series.

In the anime
Ditto's first appearance was in IL037, where in a Trainer named Duplica owned one.

Trivia

 * Ditto's cry is similar to Poliwag's.
 * Ditto makes an appearance in Super Smash Bros. Melee.
 * In Generation IV, it's possible, by glitch, for Ditto to learn copied moves permanently by transforming into a Pokémon which knows Rage.
 * If a Ditto battles a Ditto, they will both use Transform and it will restore the PP every time so the battle will never end.
 * Due to Ditto being able to Transform, Ditto is capable of breeding with any Pokémon capable of breeding and is the only Pokémon that can breed with genderless Pokémon that can breed such as Magneton and Manaphy, however all eggs received using this method will always hatch into the lowest evolutionary form of the other Pokémon regardless of the other Pokémon's gender (or Phione in the case of Manaphy).
 * Ditto can be only paralyzed when in the transformed mode.
 * Ditto is one of the few Pokémon that's name is an actual word.
 * Ditto's dictionary definition is "to duplicate".
 * Ditto is sometimes thought to be a failed attempt at cloning Mew. This is because they're both genderless, weigh 8.8 lbs., have similar base stats, are the only known Pokemon to have the ability to use the move Transform and have the same normal (pink) and shiny (blue) colors, however another theory for this is because Mew is supposed to be the Ancestor of all Pokémon therefore passed these traits onto Ditto.
 * In Pokemon Red, Ditto is also found in the lab that Mewtwo experimentation is being done, the Pokémon mansion.