In Pokémon Pokopia, Tangrowth is the only remaining resident of the withered world.
The game begins in a setting where Pokémon and humans once lived together, but the world has deteriorated and the humans are gone. Tangrowth is presented as the lone resident still living in the wasteland when Ditto awakens.
This detail establishes the game’s opening mood and explains why restoration is necessary. Instead of beginning in a thriving Pokémon town, the player encounters a largely empty landscape and gradually turns it into a welcoming habitat. Tangrowth therefore functions as an important story figure as well as part of the world-building premise.
Torterra and Trevenant are easy alternatives to imagine because both are plant-associated Pokémon. However, the opening setup specifically names Tangrowth. Later areas introduce many more Pokémon, so Tangrowth’s status refers to the world at the beginning of the story, not to the entire game’s eventual population.