Puffy is an NPC found outside the inn of Tatroi. When you talk to her, she can host an choice-based adventure game for 600 Fol. You'll need to craft a Nuclear Bomb via the Machinist Specialty in order to complete it and beat her in her own game. Here's how you can complete Puffy's mini-game.
After starting her game, choose the following:
1. Go left
2. Search the corpse
3. Let me search it already. (Obtain 120F and a Flare Bomb)
4. Keep going
5. I'll use a Flare Bomb (You’ll lose it but will get Murky Potion in return)
6. I’ll use an item (The Nuclear Bomb in your inventory will be used)
After this, you'll beat Puffy's game. You'll obtain 100SP, 600F, and Saber. Once you beat her, she won't offer the game to you anymore.