Lemon

Lemons are items found in Paper Mario. The only known location of these lemons is a tree found in The Oasis of Dry Dry Desert. Lemons replenish one HP and two FP if Mario eats it. Lemons are also used in cooking to make a tasty tonic. Mixing a Lemon and Cake Mix will create the Lemon Candy, which can heal 5 HP and 15 FP. The only way to get rid of the Anti-Guy without defeating him is to give him a Lemon Candy.

Even though the Lemon is used in cooking and for warding off the Anti-Guy, those things are only optional. The mandatory purpose of the Lemon is to give to a green nomadimouse. Then, the mouse will tell you to buy a Dried Shroom and then a Dusty Hammer in that order. If you do, you can find Moustafa, who will give the Pulse Stone to you. Because the Pulse Stone is an important item that must be gotten, finding a lemon is required.