What is the difference between the Giants knife and the Biggoron Sword?

Answer 1

The Giants Knife is breakable and it costs 200 Rupees, and you buy it from the Biggoron inside Goron's City. Biggoron's Sword is unbreakable and is acquired after quite a long quest for free from the Biggoron on the top of Death Mountian Trail.

Here is the quest to get Biggoron's Sword:

PS¹: Do not warp when you're on "time missions". If you do, you'll arrive at the Teleport Pad with only one second remaining and (obviously) you'll lose and will have to restart that "mission".

PS²: I STRONGLY recommend you to do this quest with Epona already.

Talk to the Cucco Lady and she'll give you an egg. Hatch it and go awaken Talon with it (He's in the house next to 2 stairs in Kakariko Village. Show the cucco to the Cucco Lady again and she'll give you a Super Cucco, Cojiro. Now, go to Lost Woods and (Starting from Kokiri Forest) turn left and show the punk guy Cojiro. He'll give you the Odd Mushroom. You have 3 minutes to deliver it to the old hag in a house behind the Potion Shop in Kakariko Village. She'll give you the Odd Potion. Simply go back to the same spot, in Lost Woods. "Mr. Nice Guy Caller" won't be there anymore, so give it to the girl standing there. She'll give you Poacher's Saw. Give it to the guy standing outside the tent in Gerudo Valley (Epona/Hookshot/Longshot needed to cross the broken bridge, if it's not rebuilt yet). He'll give you the Broken Goron's Sword. Give it to the Biggoron on Death Mountain's top. In trade he'll give you the Prescription. Give it to King Zora (If he's still frozen, is good to complete the Ice Cavern Quest, which can be found in a cave in Zora's Fountain, just following the icebergs. Use Blue Fire on him and, if you want, on the Zora's Shop, too). He'll trade that for a Eyeball Frog. Quickly deliver it to the Lab in Lake Hylia. After showing the crazy guy the frog, he'll give you the Big Goron's Eye Drops (I guess it's the item with the biggest name in the game LOL). Hurry up and go talk to the Biggoron. After showing him the eye drops (You'll understand when you read the conversation) he'll trade that for the Claim Checker. Then wait three whole days (That's basically singing Sun's Song 6 times), show him the Claim Checker and it's over. You now handle The Sword which deals the biggest damage on the game. Good luck now.