The Legend of Zelda: Ocarina of Time/Item Trading

In Ocarina of Time there is one main side quest: a long chain of item trading. Get item A from person A and then take it to person B to receive item B. It continues on until you get the legendary Biggoron Sword. The quest is livened up by interesting items and time limits to race to the next person. Whenever a time limit occurs, never use a warp song, because the timer will automatically hit 0.

The only requirements to get the sword is to have the Longshot and/or Epona (Epona makes the whole thing both easier and faster to complete); this means you can have the Biggoron Sword for every dungeon as an adult!. If you want to get the Hookshot first, you'll already be in Kakariko village and close to Anju (the first person in the series of trades). Also note that you will have to unfreeze King Zora: you'll need to venture a few rooms into the ice cavern to bottle up some Blue Flames, or buy some blue fire from the potion shop in either Kakariko Village (or if you're a child Hyrule Castle Town) or from Zora's Domain as a child. The entrance to the Death Mountain crater in Goron City will need to be open as well for a shortcut.

Pocket Egg
Talk to Anju (the lady allergic to chickens) as an adult. She will give you the pocket egg to take care of. Wait a day for it to hatch or just play the Sun's Song a couple times until it hatches into a Pocket Cucco.

Pocket Cucco
Take the Pocket Cucco to Talon (he should be sleeping inside a house in Kakariko Village). Pull out the Pocket Cucco and it will crow and wake him up. If you leave the building and return, Talon will have left and gone back to Lon Lon ranch. The Pocket Cucco will now be happy because it woke up an extremely lazy person. Take the Cucco back to Anju and she'll trade it for Cojiro, a rare blue chicken that was once her brother's, but now rarely crows.

Cojiro
Take the Cojiro to the slumped over man in the lost woods (head left from the Kokiri Village entrance). He will trade the Cojiro for an Odd Mushroom. The Odd Mushroom will spoil, so hurry to Kakariko Village and give it to the old hag in the potion shop.

Odd Mushroom
Take the Odd Mushroom to the old woman in the blue potion shop in Kakariko Village within three minutes. Don't warp! She will use it to create Odd Medicine. If you don't make it, you'll end up back in the Lost Woods and have to trade Cojiro again. The best way to get back to Kakariko Village is through the entrance into the Goron City in the Lost Woods. From there, run down the mountain into the Village. Just past the gate into the Village, there's a house with a blue roof above you. You can get on top of that roof with the Hookshot if you position yourself just right. Go to the railing outside the windmill door and jump on it, but be careful not to fall off. From this position you should be able to position your Hookshot so it will catch on the rooming material on top of the blue house. When you're on top of the roof, jump down into the backyard and run up the stairs to the door of the house with the blue roof. Talk to the old woman inside to trade the mushroom.

Follow the above instructions until you're back in Kakariko Village. As soon as you enter the town, look diagonally left - you'll see the red roof of a Potion Shop jutting out from the edge of the rocky wall (sadly, its not the one you're trying to get to). Get within range, pull out your Hookshot and aim it at the red portion of roof just above the point where the rock wall and the triangular wooden framing of the house intersect - as long as the red Hookshot reticule is visible while hovering over a red section of the roof you should be ok. You'll end up pulling yourself somewhat through the rock wall and onto the roof. From there, run diagonally left off the end of the roof and you will land on or near the stairs to the Potion Shop with the old hag. Go in and approach the counter, trigger the mushroom with "C," and she will reward you with the Odd Potion.
 * Alternate method

Follow the above instructions to get to Kakariko village. Once you arrive, look at the potion shop on your left. If it is night time, play the song of suns, otherwise you can just run straight in through the door. There is a back door, which will let you out to the top of a ladder. Climb or jump down, then run to the top of the nearby flight of stairs. Enter the building and press "C" to trigger the mushroom to give it to the old lady.
 * Easy method

Odd Medicine
Return to the place where you traded Cojiro. Fado, one of the Koriki girls, will be there instead. She says the man turned into a Stalfos. She demands that you give her the potion, but will give you the Poacher's Saw he left behind anyways.

Poacher's Saw
Go to the carpenter's tent in Gerudo Valley and trade this to the boss of the carpenters (if you have not yet rescued the carpenters from the Gerudo Fortress, you will need Epona or the Longshot to cross the broken bridge). He has not seen it since he left it with his wife, so he'll be shocked. He'll give you the Broken Goron's Sword in return.

Broken Goron's Sword
Take this up to the Biggoron on top of Death Mountain. He will trade the broken sword for a prescription. His eyes have been blinded by a recent eruption on the mountain, and he can't work on the sword until you clear them up for him.

Prescription
Take the prescription to King Zora (be sure to unfreeze him via a Blue Flame first). Remember that Zora's Domain has been frozen over by Ganondorf, so you won't be able to get there via the Lake Hylia shortcut. The king will take the prescription and tell you he doesn't have the medicine but does have the ingredients for it and give you a perishable Eyeball Frog. He will tell you to give it to the scientist in Lake Hylia. If you don't make it, you will automatically go back to Zora's domain and must make the Prescription transaction again.

Eyeball Frog
You must give the frog to the professor in Lake Hylia in three minutes. DO NOT WARP THERE, your clock will go down to one second left if you warp. If you can get it to the professor in time, he'll mistake it for his dinner, then make you the World's Finest Eyedrops. However, there are no preservatives in it, so it will spoil. If you don't make it, you automatically go back to Zora's domain and must make the Prescription and the Eyeball Frog trades again.

The best way to do this is to exit Zora's Domain and dive down to the shortcut to enter the Lost Woods. Exit the Woods and then the Kokiri Forest into Hyrule Field. Call Epona if you have her. If you don't have Epona, use your map to aim Link in a straight line to Lake Hylia, then turn 180 degrees. Now hold down the Z trigger (or L button if you're using GameCube, Wii classic controller, or 3DS), and run backwards to the Lake (it's faster than running forward). When you reach Lake Hylia, go to the house and talk to the professor.

Eyedrops
Now you must get back to the Biggoron within four minutes, again do not warp! The best route to take is to take Epona and ride her to the Kokiri Forest (if you don't have her, use the backward-walking method described above to get there faster). From the Kokiri Forest, enter the Lost Woods and enter the Goron City. Hop down to the lowest level of the City and enter Death Mountain Crater. Here, turn to the right and make your way to the ladder. Climb up and take the exit to the outside. Give Biggoron the drops. When you give him the Eyedrops, he uses them and gives you a Claim Check to claim the sword because it will take three days to fix the broken sword. Alternatively if you're going the normal way, if you already left the green beans once while you're a child, as an adult, you can use it to travel up to the volcanic path to where Biggoron is.

Claim Check
Either sit around patiently for three days or play the Sun's Song six times and talk to Biggoron again. When you do, you get the Biggoron's Sword from him. After getting the Claim Check, it will remain in your inventory permanently.

Biggoron's Sword
The strongest blade this game has to offer, the Biggoron's Sword itself is twice as powerful as the Master Sword. It takes two hands to wield just like the Giant's Knife, but this one doesn't break on you. You'll only run into problems when facing enemies that you need to use your shield against, like Octoroks.