Squirtle teaches Ditto Water Gun in Pokémon Pokopia.
Ditto can befriend Pokémon and learn useful moves from them. One of the clearest early examples is Squirtle’s Water Gun, which Ditto can use to water dried-up plants and help restore the environment. The move functions as a practical world-building tool rather than merely as a battle attack.
This system reflects Pokopia’s central idea of using Pokémon abilities to rebuild habitats. Bulbasaur provides a useful comparison: its Leafage can grow patches of grass. These examples make the move-teaching mechanic distinct from the conventional Pokémon method of learning attacks through leveling, items, or move tutors.
Squirtle is easy to mix up with Bulbasaur because both teach moves that help revive nature. However, Leafage belongs to Bulbasaur, while Water Gun belongs to Squirtle. The question concerns the Pokémon associated with Water Gun specifically.