Twinmold

In Majora's Mask, Giant Masked Insect: Twinmold is a pair of colossal insects found in the fourth dungeon, Stone Tower Temple. This monster is responsible for all the curses that have been placed on Ikana Canyon, and is keeping the final of the Four Giants captive. Twinmold's body is protected by an exoskeleton that leaves only its head and tail exposed.

Strategy
Link enters the boss room of the inverted Stone Tower Temple, which is actually the room where the Garo Master is fought. After he jumps into the portal in the room, he finds himself in a sand-swept, seemingly endless desert with a few stone pillars. Then, out of the sand, emerges the Giant Masked Insect: Twinmold.

To defeat Twinmold, Link must attack its vulnerable heads and tails. The most effective method for defeating Twinmold is for Link to use his Sword with the recently acquired Giant's Mask equipped, which will allow the young hero to grow to the size of Twinmold. However, Link will not be able to use Z-Targeting while using the Giant's Mask. As the Giant's Mask drains Link's Magic Meter, it is wise for Link to have Magic-replenishing Potion during the battle. Alternatively, Link can drink a bottle of Chateau Romani before the battle. This will give Link unlimited use of magic. Link can also replenish his Magic Meter by destroying the pillars found throughout the stage, which contain Magic Jars.

It is possible for Link to defeat Twinmold without the Giant's Mask by using Arrows, Bombs, or simply his sword to attack Twinmold's weak points. Ice Arrows are quite effective against Twinmold's red tail, as are Fire Arrows against its blue tail. Twinmold is also vulnerable to Fierce Deity's powerful attacks. However, Fierce Deity's Energy Beam is rather ineffective in this battle due to the fact that Twinmold is constantly in motion.

If Link strays too far from the initial platform during the battle, even if he is wearing the Giant's Mask, he will sink into the sand. This causes him to be returned to the dungeon's entrance. Twinmold may fly past this boundary in an effort to lure Link into the trap.

Once Link has dealt sufficient damage to one half of Twinmold, its body will explode, its head crashing into the sand in the distance.

Once both parts of Twinmold are defeated, Link will receive Twinmold's Remains, freeing the final Giant who was trapped in Twinmold's body. He will also receive a Heart Container. Twinmold's defeat lifts the curse on Ikana Canyon, causing the undead monsters brought to life by the curse to disappear.

Trivia

 * Twinmold bears a striking resemblance to the Lanmola of A Link to the Past.
 * Twinmold's name may be a reference to Moldorm but with the '-orm' removed and "Twin" placed in front, with 'Twin' referring to the fact that there are two of them.
 * This boss is possibly one of the largest Link has ever fought, along with Molgera, Stallord, Bongo Bongo, Morpheel, Eox, Cragma, Dark Dragon, the Demon Train, Koloktos and Tentalus.
 * Oddly, there are structures bearing the image of Majora's Mask in the desert that Twinmold is fought in.
 * Twinmold is the only boss in Majora's Mask that does not have a distinct Critical Point, the reason being its main weakness is constantly exposed.