Biggoron Sword Trading Sequence
This is a trading sequence to get the biggoron sword. You need to get Epona for this.
1. Go to the cucoo lady in Kakariko Village and
she'll give you the pocket cucoo.
2. Take this pocket cucoo to Talon who is sleeping in a house across from the archery room. Wake him up.
3. Take the pocket cucoo back to the cucoo lady
and she'll give you cojiro. 
4. Take cojiro to the place where skull kid use
to be at and give Cojiro to the man sleeping, he'll give you an odd mushroom.
5.you'll have a time limit to give the mushroom
to the potion lady at Kakariko Village. She'll give you weird potion made
out of the mushroom.
6. when you go back to give the Odd Potion to the man, he won't be there, but a girl will be and she'll give you Poacher's saw.
7. take the poacher's saw to gerudo's fortress
and take it to the boss carpenter, he'll give you the broken biggoron sword.
8. take the broken biggoron sword to the big
goron at the top of Goron's mountain and he'll give you a prescription to take
to King Zora.
9.Take the prescription to king Zora and he'll
give you an eyeball frog replace for the prescription.
10. take the eyeball frog to the professor at Lake Hylia and he'll give start working on the eye drops. once the eye drops are done, he'll give it to you and tell you to take them quickly to the big goron.
11.quickly take the eye drops to the big goron in a time frame of 5 minutes. When you give him the eye drops, he'll give you a claim check.
12. after a few days, the big goron will be done with the sword. go back to him and claim your sword.