Wart

Wart is a Mini-Boss in Majora's Mask. It is one huge eye that rolls around trying to hit its enemies. At the start of the battle, Wart is hovering slightly above the ground, completely surrounded by a mass of bubbles, which render it immune to any damage. In order to defeat the Wart, Link was forced to use his range of weapons to knock the bubbles off of Wart, then eliminate them before they could reattach themselves. If a bubble managed to reattach itself, Link would have to forcibly remove it again. When the Wart opened its eye, unobscured by its bubbles, Link could attack it, preferably with his bow, until it fell to the ground, dropping any bubbles still clinging to it. The Wart would then begin rampaging through the room, charging from wall to wall in an attempt to kill Link, but its weakness hadn't changed. After a few more arrows, Wart was defeated, leaving no corpse as it exploded, revealing the treasure it had protected.

Strategy
The Wart is a time-consuming enemy. The sheer amount of bubbles on it make it a long struggle to pierce its shield, as it is constantly moving, along with the Wart, which will differentiate from retreating to trying to press itself against Link in an attempt to cause damage. The bow is not a good idea at this point, as there are simply too many bubbles. Any offensive weapon is capable of removing the bubbles, although the best is the bomb. A good way to do this to use the Blast Mask. Although this causes damage, it can easily knock off many bubbles at once. The bubbles are incapable of being destroyed while on the Wart, only knocked off, which makes them even more of a pain. When an opening is finally made, and the Wart's eye is no longer blocked by bubbles, the bow is the way to go. After enough shots, the Wart will enter stage two, forcing its surviving bubbles off its body and begin rolling around wildly. First finishing off any bubbles, then attack the Wart with the bow. After a few more shots, the Wart will be finished.

Another strategy is to use your Hookshot and remove the bubbles one by one until few remain. After that hit the Wart's eye until it drops its remaining bubbles. Now it is easier to kill all of them. Use Z-Targeting and shoot arrows at Wart when you see its eye. This process might take a little longer, but is slightly easier.

Trivia

 * Wart also has a resemblance to Arrghus, who you kill in the same manner.
 * The Wart also appeared in the Secret Shrine, defeated in exactly the same way.
 * A frog-like character named Wart also appeared in Doki Doki Panic (or, Super Mario Bros. 2). This character differed drastically from the Wart of Majora's Mask. Interestingly, this Wart made a cameo appearance in Link's Awakening, with his japanese name, Mamu Mamu.