The Kooky Cookie is a cookie made by Tayce T. and found only in Paper Mario. The main ingredients are Cake Mix and either a Koopa Leaf, a Stinky Herb, or a Maple Syrup. It causes one of these status effects: Invisible, Electrified or Sleeping, and is intended to restore 15 FP, however, due to a programming error, if used inside of battle, the item restores 30 FP instead. It can be sold for 12 coins.
This is one of the items that Koopa Koot asks for; his specific cookie is made from Cake Mix and a Koopa Leaf, and he gives Mario one coin in return.
The Kooky Cookie can be considered similar to the Love Pudding from Paper Mario: The Thousand-Year Door, namely because both are dessert-themed items that can give Mario one of three status effects.