Gobblegut resembles a giant serpentine dragon with a row of numerous Bellyache Bulges (large pink swellings) growing from its body. Its scales have swirl designs, though its underside lacks scales, thus exposing its pink skin. Gobblegut has a few jagged crystals protruding from its head, and it has a large bulbous chin that has numerous scars on it. It also has orange eyes with a demented look to them.
The giant dragon circles the planet and eventually swoops down and crunches down on the surface of the planet in an attempt to injure Mario. When it blows steam out of its nose (making a noise akin to a train whistle), it dives down and tunnels right through the middle of the planet, thus exposing its six Bellyache Bulges to attack. The six bulges surrounding Gobblegut's body can be burst when Mario uses a spinning attack on them when they get temporarily stuck in the planet's surface while tunneling, or by doing a somersault and spin attacking a bulge. After three hits, Gobblegut becomes angrier and starts moving faster. After the last Bellyache Bulge bursts, Gobblegut slows down, burps, and completely explodes, releasing a Grand Star.
Bellyache bulges are found at various intervals along the serpentine body of Gobblegut when it is fought in Bowser Jr.'s Fiery Flotilla. They appear to be large pink swelled segments, six of which appear along Gobblegut's body. Just before Mario encounters Gobblegut for the first time, Bowser Jr. warns Gobblegut to protect them from attack. When Gobblegut burrows into the ground, the Bellyache Bulges will become stuck in the ground momentarily, at which point the player must attempt to spin each of the six Bellyache Bulges, popping them and forcibly removing them from his body. Mario can also perform a backflip and then spin to hit the Bellyache Bulges when they are above him. Each time one is destroyed, 10 Star Bits will be released, and Gobblegut will take more damage. In effect, these Bellyache Bulges act as Gobblegut's only weakness, as it cannot be damaged by any other means. When all six of Gobblegut's Bellyache Bulges have been destroyed, it will explode, and the player will win the battle.
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