Twinmold

Twinmold is a pair of humongous insects found in the fourth dungeon (Stone Tower Temple) in The Legend of Zelda: 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.

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. 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 is probably a species of Moldorm, as it resembles the Moldorm in terms of weakspots. However, it is more like the Lanmola in terms of strategy, and so may actually be a link between the two.