The Blast Mask has the capability to create explosions. Like Bombs, the Blast Mask can be used to blow up boulders and defeat various enemies. However, unlike Bombs, there is not a limited supply of explosives Link can use. One of the the only downsides is that it takes a considerable amount of time to recharge after using it. Furthermore, Link may also take recoil damage from the blast. However, this can be easily avoided by holding up his Shield so that no damage is taken.
Obtaining the Blast Mask
In North Clock Town at Midnight on the First Night, the Old Lady from Bomb Shop gets robbed by Sakon the Thief at approximately 11:15. Link can simply slash at the bag to save the Old Lady, who rewards Link with the Blast Mask.