In the course of his journey, Ash battles a mountaineer Pokémon trainer he encountered in a small wooded area. Ash deploys his Bulbasaur against the mountaineer's Rhyhorn, but Bulbasaur is behaving very strangely, causing even Pikachu to be concerned. In the end, Bulbasaur defeats Rhyhorn, but Ash decides to go immediately to a Pokémon Center and seek help from Joy. What could be the problem with Bulbasaur?