Which Pokémon teaches Ditto Surf in Pokémon Pokopia?

Lapras teaches Ditto Surf in Pokémon Pokopia.

After learning the move, Ditto can transform into a Lapras and travel across water. Surf is therefore an exploration and movement ability in Pokopia, helping the player cross waterways and reach parts of the environment that cannot be reached on foot.

The game reinterprets familiar Pokémon moves as practical tools for rebuilding and exploring. Bulbasaur's Leafage can help add greenery, while other Pokémon provide abilities connected with clearing, construction, travel, or environmental care. Lapras's association with water makes Surf a natural fit for the game's traversal system.

This answer refers specifically to the Pokémon that teaches the move in Pokopia, not to every Pokémon that can learn Surf elsewhere in the Pokémon series. In the wider franchise, Surf is associated with many Water-type Pokémon, but Pokopia highlights Lapras for this role.