Neesha used her Dewgong to go to New Island when it was actually forbidden to go due to the bad weather. Neesha then introduced her Pokémon, including Dewgong, to Ash Ketchum and his friends. Dewgong was later captured by Mewtwo by using the Mewtwo Ball. Dewgong was later freed along with the rest of the Pokémon by Ash. Dewgong then battled against the Dewgong clone.
None of Dewgong's moves are known.