Had an idea earlier of a Paper Mario game where your only partner is Peach, but she can use different powerups to transform, and those give you partner abilities. Like, when she changes forms, she'll stay like that until you transform again, so it works like traditional partners. Her personality even changes slightly based on her form.

Pop-up Peach - Pulls Mario into the book. You can move around and jump while in it, plus you can slip through narrow spots. She's more playful and fun loving


Fun little side note, her "crown" is a pull tab. When she talks and her mouth opens and closes, the tab goes up and down.