Paper Mario: The Thousand-Year Door Tips

Use 0 FP on "3 FP or less" attacks
Wear 3 badges: 2 flower savers and any number of FP drain if you want to do "3 FP or less" attacks for no FP.

The maximum FP normally required to attack for no FP is the number of FP drains plus 2 if you wear 2 Flower Savers.