The Repel Cape is an item found exclusively in Paper Mario: The Thousand-Year Door.
These capes can be purchased at the Souvenir Shop in Glitzville for 15 coins and from Charlieton. They can also be made by Zess T. by mixing a Boo's Sheet and Point Swap. Using the Repel Cape makes Mario or a Partner Dodgy for two turns, which means that enemies will fail to attack Mario or a Partner in some attacks.
The Dodgy Fog, one of Flurrie's attacks, has the same Dodgy effect as the Repel Cape. However, it lasts four turns, so it would be a better choice to use the Dodgy Fog if one wants to spare some FP or coins.