The trading sequence begins as an adult with Cucco Lady in Kakariko Village. For Cojiro, you need Epona and the conversation with Talon. Complete the early trading steps before the Forest Temple and continue the sequence after the Ice Cavern.
Pocket Cucco and Cojiro
As an adult, collect the Pocket Egg from the Cucco Lady in Kakariko Village and wait until the next morning for it to hatch. Rescue Epona at Lon Lon Ranch. Back in Kakariko, use the Pocket Cucco to wake Talon in the house near the stairs to Death Mountain Trail, then speak to him so he returns to the ranch. If you woke him earlier, speak to him again after rescuing Epona. Finally, show the Pocket Cucco to the Cucco Lady to receive Cojiro.
Odd Mushroom – four minutes
In the Lost Woods, go left from the entrance. Show Cojiro to the sleeping man. Deliver his Odd Mushroom to Granny in the back potion shop of Kakariko Village within four minutes . The route leads across the plains and through the backyard of the front potion shop. Do not use the Warp Song during the delivery.
Odd Poultice and Poacher’s Saw
Take Granny’s Odd Poultice back to the same clearing in the Lost Woods. A Kokiri girl now stands where the man was sleeping. Give her the poultice to receive the Poacher’s Saw.
Broken Sword and Prescription
Cross the destroyed bridge in Gerudo Valley with Epona or the Longshot. Give the Poacher’s Saw to the foreman outside the tent in exchange for the Broken Goron Sword. Take it to Biggoron at the top of Death Mountain. Because of his irritated eyes, he’ll first give you a Prescription for King Zora.
Eyeball Frog – two minutes and 30 seconds
Thaw King Zora with Blue Fire collected in the Ice Cavern, then show him the Prescription. Deliver his Eyeball Frog to the scientist at the Lakeside Laboratory within 2 minutes and 30 seconds. Descend the ice steps by the waterfall in Zora Domain, follow Zora River downstream, and ride Epona across Hyrule Field to Lake Hylia. Avoid warp songs during the delivery. The underwater shortcut to the lake opens after Morpha is defeated.
Specialty Eye Drops – three minutes and 30 seconds
The scientist gives you the Specialty Eye Drops and starts a 3 minute and 30 second delivery timer. Ride Epona from Lake Hylia to Kakariko Village, leave through the north gate, and climb Death Mountain Trail to Biggoron at the summit. Hand over the drops before time runs out. Avoid warp songs, which spoil the delivery.
Biggoron Receipt and Biggoron Sword
After the delivery, Biggoron gives you the Biggoron Receipt. Wait three days; play the Sun’s Song to advance between day and night. Show Biggoron the receipt to collect the unbreakable Biggoron Sword. Link needs both hands to wield it, so he cannot raise a shield while using this weapon.