Her first appearance was in Ditto's Mysterious Mansion. Ash and his friends were traveling through Kanto when they sought shelter from the rain in an abandoned mansion. The house was actually called "The House of Imite" and it was owned by Duplica and her Ditto. She showed them Ditto's ability to to transform into any Pokémon. A skeptical Ash sent out his Bulbasaur to battle Duplica's Ditto. Surprisingly enough, Bulbasaur lost against the imitation. Duplica then explained that her Ditto had trouble transforming one aspect of it: Its face. No matter what Pokémon it Transformed into, it always retained the beady eyes and wobbly mouth of a Ditto.

Team Rocket kidnapped the Ditto. They wanted to have Duplica's Ditto Transform into a Dratini so they could give it to Giovanni. After a while, they were able to train it to Transform perfectly. After Ash, Brock, Duplica, and Misty dressed up as Team Rocket and rescued Ditto, Duplica felt she was ready to open up her mansion as a theater to entertain passing Pokémon trainers.

Later, in Imitation Confrontation, Brock noticed that a Nurse Joy they were talking to was an imitation. It turned out to be Duplica, who had come to the local town for a Pokémon Acting Competition. She had another Ditto, Mini-Dit, with another problem. It could Transform into perfect replicas of other Pokémon, in every way but size. So when it transformed into an Onix, she had a tiny, hand-held Onix.

Team Rocket stole Mini-Dit and planned to have it transform into a Pokémon that they could pass off as a rare, pygmy version, so that they could get a rare and powerful Pokémon in return. Duplica recovered Mini-Dit and decided that its unusual transformations made it unique; the audience seemed to agree.

Although Duplica sometimes performs by imitating Pokémon herself, her usual shows feature her imitating a Pokémon Trainer while her Ditto imitates that trainer's Pokémon. She did an excellent impression of Ash and Nurse Joy, for instance.

(Source: Bulbapedia)