She needs rescuing by Punio and Mario, as she is locked up, with the majority of the other Punies, in a cage on the highest level of the Great Bogley Tree. She is later rescued by unlocking the cage with the red key. She then gives Punio a Dried Shroom, which had originally been an ordinary Mushroom, but after long hours in the cage, it shriveled up and thus a Dried Shroom was made. Punio eats it but nearly chokes on it; he hides this choking by saying that it was "delicious *Gag*".
Petuni participates in the 101 Punies that helps Mario through the Great Tree, though she cannot always be seen in the group. Petuni is with the rest of the Punies when Mario leaves, and appears at the games end where she along with Punio gives Mario and Peach mushrooms.
After chapter two and Mario has saved the Great Tree, he can play "Stump Petuni", a game in which Mario asks Petuni questions. If Mario asks her the question, "Mario likes which person the most?" Petuni should answer "Princess Peach" and gives Mario a Mystic Egg. If Mario asks her any other question, she will not know the answer.