Which Pokémon does Ditto meet first in Pokémon Pokopia’s story?

Ditto first meets Tangrowth in Pokémon Pokopia’s story.

The Tangrowth is known as Professor Tangrowth and has taken responsibility for studying the damaged environment. After Ditto finds an old Pokédex and adopts a human-like form, this meeting begins the partnership that drives the game's restoration effort.

Professor Tangrowth helps establish the story's central mystery: why humans and Pokémon disappeared from the once-inhabitable world. Rather than sending Ditto into a conventional battle quest, Tangrowth directs the character toward rebuilding habitats and helping the surviving Pokémon population.

Tangrowth is easy to confuse with other major Pokémon in the opening sections. Squirtle is encountered soon afterward and needs help recovering from dehydration, but Tangrowth is the first Pokémon Ditto meets in the plot.