The Zora Mask, to help Link swim underwater without needing to breathe.

Link knew that he was going to the Water Temple next, so the Zora Mask made the most sense to him. He told the Mask Salesman that, and he handed him the requested mask.

"Good choice, yes yes! Try it on, please!" the salesman said, and Link did want to see how the mask worked. He lifted it up to his face, and...