Kamaro's Mask is one of the twenty four Masks from Majora's Mask. Kamaro's Mask is received after talking to Kamaro. Kamaro can be found on one of the mushroom-shaped rocks in the snowy region of northern Termina Field.
When Link wears Kamaro's Mask, it gives him the ability to dance like Kamaro's spirit.
If Link goes to West Clock Town at night, he will find the Rosa Sisters trying to choreograph a dance for the Carnival of Time. If Link stands in front of them and performs the dance, they will learn it, and as a token of gratitude give Link a Piece of Heart.