From the Super Mario Wiki
In The Super Mario Bros. Super Show! episode "The Fire of Hercufleas", Mario, Luigi, Toad and Princess Toadstool, needing help to defeat the evil King Koopa, decided to ask Hercufleas for his assistance in overthrowing King Koopa. When Mario, Luigi, Toad and Princess Toadstool arrived at Hercufleas' home in Mythis, they discovered that Hercufleas, through overeating, had become incredibly obese.
Finding Hercufleas slumped in a chair, surrounded by donuts, Princess Toadstool began to doubt that Hercufleas could aid her in beating King Koopa. Ignoring Princess Toadstool's doubts, Toad greeted Hercufleas and learned from the dumpy hero that he didn't work as a hero anymore, instead, Hercufleas now worked as the guardian of the Great Balls of Fire.
After showing Mario, Luigi, Toad and Princess Toadstool the Great Balls of Fire, Hercufleas told them that he wouldn't be able to help them defeat King Koopa, saying he wasn't much of a hero anymore. As Toad tried to reassure Hercufleas, several Beezos, sent to steal the Great Balls of Fire for King Koopa, appeared. Seeing that these Beezos were trying to steal the Great Balls of Fire, Hercufleas tried to stop them, only to be whacked aside by the Beezos, who struck Hercufleas in the head with the urn containing the Great Balls of Fire.
Getting off the ground, Hercufleas tried to chase the fleeing Beezos, only to run out of breath. As Hercufleas was left panting on the stairs of his acropolis, a Beezo flew over to him and mocking Hercufleas, tied his legs together and pushed him down several stairs, causing Hercufleas to crash into a statue of his much fitter self.
Some time later, Mario and Luigi, who had just returned from an unsuccessfull attempt to get the Great Balls of Fire back from King Koopa, tried to cheer-up a depressed Hercufleas. As Mario and Luigi talked to Hercufleas, they manage to convince him to allow them to train him and get him into batter shape. At first, Hercufleas did horrible at his training, failing at jogging, chin-ups and jumping-jacks, though Hercufleas eventually does get better. After a lot of training, Hercufleas manages to get back into shape and decides to help Mario, Luigi, Toad and Princess Toadstool in defeating King Koopa.
Shortly after arriving at the Koopacropolis, Hercufleas, Mario, Luigi and Princess Toadstool could only watch as a Beezo attempted to dump Toad into the Great Balls of Fire, under King Koopa's command. As Toad was dropped on top of the Great Balls of Fire, Hercufleas, grabbing a tray of marshmallows from the nearby Mouser, threw it over the top of the urn the Great Balls of Fire were in, saving Toad; with Toad saved, King Koopa's Beezo minions were captured when, after trying to re-capture Toad, they accidentally flew into the marshmallows that softened Toad's landing, becoming stuck in them.
King Koopa, becoming enraged, began trying to defeat Hercufleas by shooting the Great Balls of Fire at him; Hercufleas managed to easily knock these Great Balls of Fire away though, by using a pillar as a bat. Unfortunately, as Hercufleas, Mario and Luigi knocked away the Great Balls of Fire, Toad was knocked off the Koopacropolis. Lucklily, Toad managed to grab a nearby Fire Flower, becoming Super Toad. With his newfound powers, Toad began to battle King Koopa as Mario, Luigi, Princess Toadstool and Hercufleas looked on.
Eventually King Koopa was defeated and Hercufleas, Toad, Mario, Luigi and Princess Toadstool returned to Hercufleas' acropolis, where Hercufleas and Toad were congratulated for driving King Koopa out of Mythis.