When the Links enter the boss room, a short cutscene shows the Big Moldorm bouncing around the pit and the large, brown block, beginning the battle. Like in A Link to the Past, the Links must proceed to jump down onto the floor to battle the boss. Similarly to Moldorm in A Link to the Past, the Big Moldorm moves randomly along the ground floor, attempting to bump into Link and knock him down to the floor below. Outside of simply running into Link, the boss does not have a formal attack.
If the Links get hit by the Big Moldorm and fall to the room below, they can find six jars that contain hearts and Force Gems. The Links can then climb a series of ladders in order to battle the boss again. Unlike in A Link to the Past and Link's Awakening, the battle with the Big Moldorm does not start over as a result of the Game Boy Advance SP screen feature.
Much like Moldorm, Big Moldorms can only be harmed by striking its tail with a Sword. However, the color of the Big Moldorm's tail can be Purple, Red, Blue, or Green, so only the corresponding colored Link can attack the tail. After a successful strike, the tail rotates colors until it settles on a new color. Eventually, it splits into two Big Moldorms once the Links have damaged it enough, but the strategy to defeat both of these is the same. When they defeat one of the Big Moldorms, it explodes, giving the Links more Force Gems. Once the Links have defeated both Big Moldorms, the path to the Trident's resting place and the Purple Shrine Maiden is revealed.
- ↑ "The Big Moldorm's tail changes color and is vulnerable only to a sword swipe from the Link of the same color." — Nintendo Power Four Swords Adventures Strategy Guide, pg. 77