The Gerudo Mask, to help Link evade capture in the Gerudo Fortress.

Link explained to the salesman that he'd been wanting to enter the Gerudo Fortress, he kept getting caught by them. He remembered that the salesman owned a Gerudo mask, and maybe that magic he was talking about would help him sneak through easier. The Happy Mask Salesman's eyes seemed to grow brighter, and he nodded excitedly. "Oh, yes, yes! That would work very well! And since I owe you a debt, I'll let you have the mask for free." Without reaching into his bag, the salesman just handed Link the wooden Gerudo mask, even though Link couldn't tell how it had gotten into the salesman's once empty hands. "I am glad to have helped you, young boy. I hope we see each other again, soon." Link was staring at the contours on the mask, and when he looked up from it the salesman was gone. Holding the mask, Link thought about it and decided to wear it now, see what it did.