The Deku Business Scrub at Hyrule Field in Zelda: Ocarina of Time Remake offers a Heart Piece for 100 Rupees. However, he will not sell the Heart Piece until you provide him with the right password. The password can be obtained by switching between Child Link and Adult Link and entering a secret grotto near Hyrule Castle Town. Here’s how to find the password and get the Heart Piece.
Where To Find The Scrub

Heart Piece One in Hyrule Field is bought from the Deku Business Scrub for 100 Rupees. The trick is that you cannot simply approach him and purchase this item; first, you will have to find the right password for him, and for this, some time travel is required.

First, make sure you have conquered the Forest Temple as Adult Link. Then go to the eastern side of Hyrule Castle Town’s gate, and you will see a cracked stone near the moat. Break it with the help of Bombs or the Megaton Hammer, and you will gain access to a secret grotto.
Once there, you will meet the Deku Business Scrub. He will not sell you anything until you tell him the right password. You can do this as either Child Link or Adult Link.
How To Get The Password

First, leave the grotto and make sure you’re playing as Adult Link. Look for a nearby tree that only appears when you’re an adult. You’ll find a Gossip Stone next to it, which reveals the password after you interact with it. However, there’s a small catch. The Deku Business Scrub has already sold his stock to the same fairy who knows the password. Don’t worry, though. You can still get the Heart Piece by using a little trick.
How To Use The Password
Go back to the Temple of Time and place the Master Sword on the pedestal to revert to Child Link. After reverting to Child Link, go back to the grotto. Speak to the Deku Business Scrub and give him the password you acquired previously. He will finally agree to give you the Heart Piece for 100 Rupees. Give him the money, and you will have collected yet another Heart Piece.
