Petuni

Petuni is Punio's little sister in Paper Mario: The Thousand-Year Door. She eventually needs rescuing from Punio and Mario and can be easily rescued with a key, then she will proceed with giving Punio a Dried Shroom (originally an ordinary Mushroom) she had been saving him. Other than that, she hasn't the most activity within the game, but plays a fair part of importance to Punio's well-being.

Mario can play "stump Petuni." Say "Mario likes which person the most?" She will say Princess Peach and will give the plumber a Mystic Egg. If Mario asks her any other question she will not know the answer.

Petuni participates in the "101 Puni group" that helps Mario through the Great Tree, though she cannot always be seen in the group for an unknown reason or glitch.

Petuni appears at the games end where she along with Punio gives Mario and Peach mushrooms.

Trivia

 * Petuni's name is a portmanteau of "Puni" and "petunia", a type of flower not to be confused with the Petunia from Paper Mario.