"That is the Bremen Mask, isn't it? If you have that, then it would appear that you have the qualities of a leader." -Happy Mask Salesman
This mask was given to Link by the musician Guru-Guru. Guru-Guru said that he stole the mask from a dog who was the leader of an Animal Troupe. Guru-Guru was jealous and stole the leader's mask. He gives the mask to Link to be cleanse of his crimes.
To march hold B. The mask can be used to get various animals to march behind Link. Burt mainly is to use to help Grog. He has one regret and that is not seeing his chicks become roosters. If Link gets all the chicks to march with him, they will become adults. Grog will give Link the Bunny's hood as appreciation.
Also as a bit of side fun, the Bremen Mask can also be used to lead the Iglo's servants in the Ancient Castle of Ikana. This will not help Link in any way, seeing how Link is unable to lead them into direct sunlight and they immediately attack Link once he stops marching.