That's the Garo Master...
The Garo Master is a Garo general and a deadly assassin that makes his first and only appearance in Majora's Mask. He serves as one of three Mini-Bosses of Stone Tower Temple, the fourth dungeon in Majora's Mask. He later appears in the Secret Shrine and in the Twinmold section of the Moon.
Garo Master has two attacks during this fight. In his first attack, he disappears, and then drops down from the ceiling to attack Link. In the second attack, he charges at Link, and sometimes disappears afterwards. To dodge his dropping attack, keep moving until he drops down, and to dodge his charging attack, keep sidestepping. Attacking him directly will do nothing, as he blocks all of Link's attacks. To damage him, Link should wait until he finishes attacking. He will then lower his guard and look for Link, giving him a chance to strike.
Once defeated, he will take out a bomb and commit a form of seppuku, blowing himself up. In Stone Tower Temple, he will tell Link that he needs to use the sacred golden light to strike the red emblem outside the temple, which will flip the dungeon, before killing himself. Link is then rewarded with Light Arrows.