The mask is given to Link by the spirit of Kamaro. Kamaro appears in Termina Field near the Snowhead area on top of a mushroom-like tree. He appears between midnight and 4 AM on the First or Second Day, where some music can be heard. Kamaro is afraid that his dance moves will never be passed down to the new generation, and asks that Link rest his soul. By playing the "Song of Healing," his musical talent will be encased inside the mask. He entrusts the hero with his final request, to spread his dance across the world.
The mask, when worn, allows Link to perform Kamaro's dance. While in West Clock Town at night, Link can find the Rosa Sisters trying to come up with a dance for the Carnival of Time. If Link stands in front of them and performs the dance, they will learn it and thank him, calling Link "master" and giving him a Piece of Heart.
The music heard near the Rosa sisters and Kamaro is the same, even though the dances are different.
Kamaro's Mask in Majora's Mask
Link obtaining Kamaro's Mask in Majora's Mask
Ghirahim wearing Kamaro's Mask in Hyrule Warriors
↑"The spirit of a charismatic dancer who died in Termina Field dances there night after night." — Gossip Stone (Majora's Mask)
↑"I am no longer part of the living...My sadness to the moon... I haven't left my dance to the world...I am filled with regret. (Translation) I am disappointed, oh moon. I have died! Oh, I planned to bring the world together and stir it into a giant melting pot with my dance! If only I had taught my new dance to someone..." — Kamaro (Majora's Mask)
↑"Spread my dance across the world... Train its followers... (Translation) I have taught it to you, now make it into a popular dance craze! I am counting on you. (Translation) I am counting on you." — Kamaro (Majora's Mask)
↑"Thank you for teaching us those steps. You are our master! Master! You're so cool!" — Rosa Sisters (Majora's Mask)