Manaphy teaches Ditto the Diving move in Pokémon Pokopia.
Diving expands the game beyond the original land-based restoration work. Once the feature is available, Ditto can enter underwater areas that were previously unreachable, opening access to aquatic Pokémon, new scenery, and underwater furniture.
The move is connected to the game’s later underwater content and to the first expansion-pass part, Bubbly Basin. The free update makes the diving ability available, while the paid expansion adds the dedicated underwater village and its associated content.
Manaphy is a Water-type Pokémon known for its connection to the sea, but this question concerns its specific role in Pokopia. Lapras, Lanturn, and Vaporeon are plausible aquatic choices, yet the game identifies Manaphy as the Pokémon that teaches Ditto Diving.