Gomess

Gomess is one of the many evils of the Stone Tower Temple in Majora's Mask. He guarded the Boss Key that Link needs to gain access to Twinmold's lair, and did not surrender it easily. He is a master with the scythe he wields.

When Gomess appeared before Link, a swarm of Bad Bats that filled the room previously flocked to his body, defending him from almost all of Link's attacks. As quickly as Link dealt with the Bats, there was always more, drawn by their master to do away with the intruder. It was almost impossible to penetrate the shroud of Bad Bats with his sword alone, and Gomess was proving more than adapt with the scythe it held, so Link was forced to turn to other means to assist him. Eventually, he found two ways of dispersing the Bad Bats: bombs, and Light Arrows. When Link used either of these, the Bad Bats would scatter, leaving Gomess vulnerable to attack. After a drawn-out battle, Gomess was eventually struck down, leaving the Bad Bats without a known master and the Boss Key without a guardian.

Strategy
Gomess is almost completely immune to harm with the sword while the Bad Bats cover its body; only a very lucky hit will penetrate. To disperse the cloud, bombs and Light Arrows are the way to go. When the Bats are scattered, attack Gomess with a weapon of choice. Repeat this pattern until Gomess is defeated.

Trivia

 * Gomess is more demonic in its appearance than many other enemies in Majora's Mask.
 * Since every undead creature in Ikana was once alive before the doors of Stone Tower Temple were opened, and Gomess appears to be a ghost of some sort, it is possible that Gomess was once a normal living being. If anything, Gomess, just like the Garo, was an enemy of the Ikana royal family, because his scyth has a decapitated skull of an Ikana Soldier on top of it.
 * Other entity made up of bat-like creatures in the Zelda series includes the Vire that appears in The Legend of Zelda, Link's Awakening and the Oracle series, and the Darknut boss of Link's Crossbow Training.
 * Out of the Zelda series, Gomess shares similarities with Death, a recurring boss in the Castlevania series. The Pokemon Darkrai has also an appearance similar to that of Gomess.