From the Super Mario Wiki
Ruby is an elderly Flopsider from the game Super Paper Mario. She lives on the first floor of Flopside, a mirror image of the town of Flipside. In her younger days, Ruby was a beauty queen. She can usually be found extolling secrets of longevity to her young granddaughter, Mitsy. Ruby is the Flopside counterpart of Pearl, and the advice both of them share with their respective granddaughters is usually the exact opposite of each other.