Nurse Joy's Pikachu used their electricity to act as a backup power generator when Team Rocket cut off the main power source at the Viridian City Pokémon Center. They then helped to defend Ash Ketchum
and Ash's Pikachu
who were being attacked by James's Koffing
and Jessie's Ekans
. Ultimately, with the help of Ash's Pikachu
they were able to thwart Team Rocket's plans and help prevent them from stealing any of the Pokémon stored at the Pokémon Center.