"This massive monster swims beneath the desert's sand. It is a subspecies of Molduga that stored up a great deal of energy by sleeping underground for hundreds of years. Its power is superior to Molduga, as its skin is rich with iron and acts as a protective shield."
The Molduking is the strongest of all Molduga, and has a slightly different coloring. There is only one in the game, being a part of the second DLC pack: The Champions' Ballad. It is found to the south of the East Barrens in the Gerudo Desert. Upon defeat, it will drop three chests, as well as an array of weapons, such as the Golden Claymore. It will also provide access to the Keive Tala Shrine.
This boss swims underneath the sand, and is practically identical to its little brother, the Molduga. It has extremely good hearing, so if you move quickly it will be alerted and begin to swim to you. The best thing to do here is to stand on land which isn't sand, such as a broken pillar or a rock. You can use its hearing to your advantage though, by standing on a rock and tossing out a Bomb in its direction. It should notice it, and begin swimming toward it. Once it reaches it, the Molduking will jump out of the sand, swallowing the bomb. At this point, you should detonate the bomb and the boss will fall to the ground, vulnerable to hits. This enemy has a very high defense, and regular sword slashes will not deal a lot of damage. The trick here is to utilise Urbosa's Fury, which deals a great amount of damage. Using this in conjunction with a powerful two-handed weapon like a Royal Claymore will deal sound damage. Repeat this process a few times to take down the boss.