This Venusaur is a grass/poison-type Pokémon that May caught as a Bulbasaur. It is the third Pokémon caught by May, and her fourth Pokémon acquired overall.
Advanced Generation series
Venusaur was caught as a little Bulbasaur which lived with many grass Pokémon on a special territory. As May ends up in the forbidden area she is chased by the grass Pokémon, but is saved by the little Bulbasaur who eventually joins her team when May is about to leave. Bulbasaur came as a big help to her team with the learned move Petal Dance which was used with a lot of elegance.
She was sent out by May in Hokey Poké Balls to enjoy the sightings of the city, though she was distracted by some flowers in a truck but was eventually rescued as the truck speeds of. She was taken to Professor Oak in the Pokémon Center and Ash later arrives. However, the Poké Balls were stolen by Team Rocket so she teams up with Ash's Bulbasaur to stop them.
She later appears in Cruisin' for a Losin'. While she is waiting in the backstage, May has a short argument with Ash, saying that she cares a lot for Bulbasaur. May's anger made her confused. When it was May's turn. She was called in to battle Lairon. However, she gets scared since she is not used to being in a stage fight. She reluctantly battles Lairon but gets knocked out, causing her trainer to lose the match.
Diamond and Pearl series
Bulbasaur acknowledged Ash's Bulbasaur as the two are good friends. May makes a comeback in Sinnoh saga revealing her new Pokémon and discovers that Bulbasaur evolved twice during her trainer's journey in Johto.