Preparation
Before the fight, upgrade your fishing rod and primary weapon to the best tier available at the current shop NPC, and bring healing consumables for at least two attempts. In co-op, agree on who is on crowd control and who is on damage before you start — switching mid-fight is usually worse than a slow first attempt.
Strategy
The Pufferfish Boss is built around motion. Watch its momentum before committing to a stance. When it charges, give it line; when it tires, take it back. The kill is a sequence of give-and-take, not a single reel. Save your strongest consumable for the second half of the fight, when the boss's patterns shift. For frame-by-frame mechanics, watch the linked video walkthroughs listed in our sources.
Co-op Roles
In a 2–4 player group, the cleanest split is one player on the line and one player on weapons. In a 4-player group, add a dedicated healer and a flanker whose only job is to bait the boss into the line player's strike zone. Avoid stacking damage dealers — the boss punishes clustered targets more than spread-out ones.
Rewards
Defeating the Pufferfish Boss unlocks progression to the next island and grants rare fish and crafting materials used in higher-tier gear. Exact loot varies between runs, but the unlock alone is worth the preparation.