Ocarina of Time Trading Sequence

This side quest results in Link being given the Biggoron's Sword. You have to be an adult and to have freed Epona to accomplish this sequence.

Cojiro
The first step is to get Cojiro from the cucco lady in Kakariko Village. If you haven't already gotten the egg from her and hatched it to wake Talon (he is sleeping in a house in the village), do so. Talk to Talon, then return back to the lady and she will give you Cojiro.

Odd Mushroom
Now take Cojiro to the Lost Woods. Take your first left upon entering the forest and present Cojiro to the guy sitting by the stump. He will in turn give you the Odd Mushroom.

Potion
Now you will be timed for this part. You have to take the Odd Mushroom to the potion shop in Kakariko Village. But when you get there, go out the back door, up the stairs, and into the shop with the old lady. After she smells it, she will give you a potion she made with it.

Poacher's Saw
Return to the Lost Woods. A Kokiri girl will now be there. If you give her the potion, she will in turn give you the Poacher's Saw.

Broken Goron Sword
Now make your way to Gerudo Valley. Jump the canyon with Epona and stop at the Boss Carpenter's tent. Give him the saw and you will receive the Broken Goron Sword.

Prescription Card
Take the broken sword to Biggoron on top of Death Mountain. He would gladly repair the sword for you, but he is having eye trouble. He gives you a Prescription Card for some eye drops.

Eyeball Frog
Travel to Zora's Domain. Present the Prescription Card to King Zora (he will need to be unfrozen with Blue Fire if you haven't done so already). He will give you the Eyeball Frog. Once again, time is of the essence.

Eyedrops
Head to the Lakeside Laboratory as quickly as you can (it is quicker to just ride the river from Zora's Domain to Hyrule Field, and then jump and Epona and ride her to Lake Hylia). Give the scientist the frog and he will make the Eyedrops for you.

Claim Check
Again, get to the top of Death Mountain as fast as possible. Give Biggoron his much needed eye drops, and he is then prepared to start work on the sword. He will give you a Claim Check in the mean time. Return in a few days time.

Biggoron's Sword
After you return a few days later, it will finally be finished.