The Garo's Mask may be acquired at any point after Link learns Epona's Song.
After calling for Epona by playing Epona's Song, Link may ride it into the Gorman Track and speak to one of the brothers while on Epona's back. They laugh at Epona, and challenge Link to a race for 10 Rupees. If Link wins the race, they reluctantly turn over the mask, convincing each other that, being only a child, Link would not understand the mask's purpose.
The Garo's Mask is required to enter Ikana Canyon. When wearing the mask at the base of the cliff wall, the mysterious figure atop the cliff, named the Poe Collector, comments on the mask, advising Link to use it to ask the regrets of the wandering spirits in Ikana.
While in Ikana Canyon, Tatl occasionally comments on a thirst for blood in the air around them. If Link equips the Garo's Mask in these areas, a Garo Robe appears, believing Link to be the Garo Master. Upon realizing he is not, the Robe attacks, and offers advice before departing.