The complete Pokemon RBY pokedex, part 13

Pokémon Name: Ditto
Type: Normal
Classification: Transform Pokemon
Pokédex Number: 132
Ability: Limber
Dream World ability: Imposter
Useful Attacks: Uh, Transform?
Location Found:
Diamond/Pearl: Route 218 (Poke Radar)
Platinum: Trophy Garden (post-National 'dex, daily Pokemon via talking to Mr. Backlot)
HG/SS: Routes 35 and 47, Cerulean Cave, Safari Zone (Wetland)
B/W: Giant Chasm Crater Forest

Ditto can copy the moves of other Pokemon, but it's most known for its breeding bonuses.