Twinmold

Giant Masked Insect: Twinmold (ツインモルド, Tsuinmorudo) is a pair of gargantuan insects found in the fourth dungeon (Stone Tower Temple) in Majora's Mask. This monster is responsible for all the curses that have been placed on Ikana Canyon, and it is keeping the fourth giant from its freedom. Twinmold's name is obviously a reference to Moldorm.

Strategy
Twinmold is defeated by Link, who must hit their heads and tails. This can be done as normal Link by Z-Targeting it and using arrows, bombs, or the sword to attack. Alternately, Twinmold can also be defeated by using the Giant's Mask (recently acquired), and the sword to even out the size difference. Your chances of scoring a hit improve tremendously while wearing the Giant's mask. (The only flaw is that Z-Targeting is disabled.) Using the Giant's Mask also greatly drains your magical energy. If you plan on wearing the Giant's Mask make sure that you have a lot of potions with you, or a better approach would be to drink a bottle of Chateau Romani before the battle, which will suspend the consumption of Link's Magic Meter and make it last forever. If you do not choose to use Chateau Romani you can find magic jars after destroying the pillars found throughout the stage. If you find yourself in the situation in which you are out of magic and you have no way of restoring it, you can use arrows. Fierce Deity's magic attacks are also an option, preferably with infinite magic power, as this approach can take some time, as the accuracy of the attacks can be horrific. After defeating Twinmold, their bodies will explode and their heads will crash into the sand. Your reward is one full Heart Container and Twinmold's Remains.

Trivia

 * Twinmold bears a striking resemblance to the Lanmolas of A Link to the Past.
 * These are possibly the largest bosses Link has ever fought, along with Molgera, Morpheel, Eox and Dark Dragon.