In the dark world on top of the pyramid go down and u will see a crack in the wall (u wont be able to blow it up with your regular bombs) go to your house in the dark world and there should be a super bomb for u to buy, buy it then take it to the pyramid and blow the wall with the crack in the wall up go in and throw your sword in the fat fairy will then give it back to u but when she does she will upgrade it and it will turn gold!!! tada