Using the Lens of Truth, Link can see a Clock Town guard at the southern end of the base of the cliff wall in Ikana Canyon. The guard's name is Shiro, and he explains that he has been stuck there for many years, and nobody had stopped to take notice of him. He thinks this is because his appearance is as dull as a stone. He asks Link for a medicine that fills him with energy. If Link gives him Red Potion, Shiro gets his strength back and stands up, thanking Link and handing over the Stone Mask in return.
While wearing the Stone Mask, Link will not be attacked by common enemies. In addition, he will go unseen by Gerudo Pirates at the Pirates' Fortress in Great Bay Coast, allowing him to walk by without fear of being thrown out. By equipping the Stone Mask, many sets of common enemies throughout the entire game can be skipped making this mask one of the most useful non-transformation masks in the game. The Stone Mask also prevents Leevers from spawning when Link walks on areas that would typically spawn them.
The Stone Mask is not universal, as certain enemies still attack Link; for example, the Gerudo Pirates in the Pirates' Fortress, who also comment on the mask, noting that it doesn't fool them.