Quest for Biggoron's Sword

In The Legend of Zelda: Ocarina of Time, Link can complete an optional trade quest in order to obtain Biggoron's Sword. In order to complete it, Link must trade many different items to people all over Hyrule. This quest can only be undertaken during while Link is an adult.

Kakariko Village
If Link talks to Anju in Kakariko Village, she will tell him that she has successfully managed to create a new breed of Cucco, one that she can touch without getting an allergic reaction. Thinking that Link might be a good Cucco keeper, she presents him with a Pocket Egg that, when incubated long enough, hatches a Pocket Cucco. Anju requests that once hatched, the Pocket Cucco is used to awaken a very heavy sleeper.

Kakariko Village
Once a Pocket Cucco has hatched from the egg on the morning of the day after he has received the egg, he can use the Pocket Cucco to awaken the sleeping Talon in a house in Kakariko Village. Upon returning to her, Anju is pleased to see that her Pocket Cucco managed to awaken a heavy sleeper and presents Link with a special Cucco known as Cojiro, which belonged to her brother, Grog. However, since being separated from its brother, Cojiro has never crowed.

Lost Woods
If Link enters the Lost Woods, Cojiro will start crowing. Resting in a forest clearing to the left of the entrance is Grog. He will initially act callous towards Link, but if Link gives him Cojiro, he will be pleased, recognizing Link as a true "nice guy" like himself. He requests that Link delivers an Odd Mushroom to the old woman in Kakariko Village for her, so that she can make a potion for him. However, the Odd Mushroom will be spoiled if taken outside of the Lost Woods for too long, so it must be delivered to the old woman within a certain time limit.

Kakariko Village
Link can enter the old woman's potion shop in Kakariko Village by passing through what was a shop when Link was young. The old woman will make Odd Potion from the Odd Mushroom, however, she remarks that the potion will not work on a monster.

Lost Woods
Upon Link's return to the Lost Woods, Grog is nowhere to be found and Fado can be found near the stump where he was sitting. She tells Link that everyone who enters the Lost Woods will eventually become lost and transform into monsters known as Stalfos. Upon seeing the Odd Potion, she tells Link that since it was made from materials native to Kokiri Forest, it must be returned. In return for the Odd Potion, she gives Link a Poacher's Saw that was left behind by Grog.

Gerudo Valley
If Link manages to cross the broken bridge in Gerudo Valley (either with the help of Epona or the Longshot) the Poacher's Saw can be delivered to Mutoh who is standing outside the carpenters' tent. Mutoh is surprised to see his long-lost tool and remarks that he thought he had left it behind with his mother, indicating that the old woman is indeed his mother. He gives Link the Broken Goron's Sword in exchange for the return of his saw.

Death Mountain Summit
On the summit of Death Mountain lives the greatest sword-smith in Hyrule, Biggoron. However, since Ganondorf resurrected the evil dragon Volvagia and caused the volcano to be active again, Biggoron's eyes were hit by an eruption, disabling him from seeing. In order to clear his aching eyes, he needs Eye Drops. He asks Link to deliver a Prescription to King Zora in Zora's Domain.

Zora's Domain
After King Zora has been thawed out of the Red Ice he was encased in with Blue Fire, Link can deliver the Prescription to him. Link receives an Eyeball Frog, a creature with many medicinal properties native to Zora's Domain. This is needed for the Eye Drops. However, once taken outside of Zora's Domain, the Eyeball Frog will be spoiled and useless once enough time has passed. Link must deliver it to the Marine Biologist in the Lakeside Laboratory near the waters of Lake Hylia.

Lake Hylia
Inside the Lakeside Laboratory, once given to the Marine Biologist, he will mistake it as a present to him and is disappointed to know that he will not be able to cook the frog's eyeballs for his dinner. Despite this, he still uses the frog to create Eye Drops for Biggoron. However, since the medicine has no preservatives in it, it will be spoiled and useless if not used within five minutes.

Death Mountain Summit
Link must travel as fast as possible in order to make it up Death Mountain and deliver the Eye Drops to Biggoron. Once delivered, Biggoron is relieved to finally be able to see again. If Link shows him the broken Biggoron's Sword, Biggoron will agree to repair it as repayment for the Eye Drops. Biggoron remarks that the process will take some time, however, and presents Link with a Claim Check so that he doesn't forget about it all together. After three days and nights have passed, Biggoron's Sword will be complete once more and Link will have obtained the strongest sword in the game.