Happy Flower is a badge that slowly and automatically restores FP to Mario during battle.
In Paper Mario, it can be traded from Merlow for 8 Star Pieces. It can also be found in Flower Fields. It uses 3 BP.
In Paper Mario: The Thousand-Year Door, it can be purchased at the Lovely Howz of Badges for 150 coins. It can also be traded from Dazzle for 4 Star Pieces.
In Paper Mario