Paper Mario: The Origami King lets you partner up with a number of different characters along the way, but the source code for the game shows that Nintendo might have had plans for one more partner that didn't make the cut.
During your adventure, you'll come across a Sombrero Guy that needs some help with a party. It's a short, but enjoyable mission, but there might be a hint in the game's source code that there were bigger plans for the character. Screwing with the game's values allows you to have the Sombrero Guy join up with you, and he follows along beside Mario.
Whether Sombrero Guy was planned for a more substantial role is unknown. Perhaps his mission was slightly different originally, and it involved him tagging along with Mario for a short amount of time. Either way, it's clear Nintendo scrapped some of their plans for the character during development.