From the Super Mario Wiki
In The Super Mario Bros. Super Show! episode "Rolling Down the River", Mark Twang apparently agrees to a race with Captain Koopa and his Sinister Star, with whoever winning the race becoming King of the River and presumably, the River World. Unfortunately, the engine of the Ding Bell was sabotaged by Captain Koopa, severally limiting the speed which Mark Twang could travel at on the Ding Bell.
While feebly trying to catch-up to Captain Koopa and the Sinister Star, Mark Twang happened too, by chance, find Mario and Luigi in the river. With a lasso, Mark Twang managed to pull Mario and Luigi aboard the Ding Bell, narrowly saving them from being devoured by a Trouter. Mark Twang was then told by Mario and Luigi that they were trying to rescue Princess Toadstool, who had been kidnapped by Captain Koopa and was being held onboard the Sinister Star.
After hearing Mario and Luigi's story, Mark Twang told them his own, about his race against Captain Koopa; deciding to aid Mark Twang, Mario and Luigi began to work on the engine of the Ding Bell.
After the Ding Bell's engine was repaired, Mark Twang, along with Mario and Luigi, began to catch-up to Captain Koopa and the Sinister Star; only to be met with another obstacle, an unpassable black pit created by Captain Koopa and a Black Pit Bob-omb. After narrowly managing to escape the current of the black pit, thanks to Mario and Luigi using a plunger to anchor the Ding Bell, Mark Twang, along with Mario and Luigi, decided to venture onto land to seak the advice of the Mouth of the River to help them pass the black pit.
Finding the Mouth of the River, Mark Twang, Mario and Luigi gained some cryptic advice to help them pass the black pit. Watching as Mario and Luigi created a large piping system, Mark Twang was surprised when that piping system managed to drain the water surrounding the black pit and emptied it in a nearby path, separated from the black pit by a wall of rocks. Mark Twang, with Mario, Luigi and the Mouth of the River easily managed to pass the Ding Bell through this newly created path.
Later, Mark Twang, with Super Mario and Super Luigi, who powered the Ding Bell ahead with pumps, managed to catch-up to and pull along side the Sinister Star. As Mario and Luigi leaped from the Ding Bell to the Sinister Star, Mark Twang had the Ding Bell zoom ahead of the Sinister Star.
Afterwards, as Mario was about to be forced overboard by Captain Koopa on the Sinister Star, the Ding Bell, supposedly driven by Mark Twang, appeared. As Mark Twang maneuvered the Ding Bell, the Mouth of the River used the Ding Bell's cannon to launch Turnips at the Sinister Star.
In the end, the Sinister Star was crashed into a beach and Mario and Luigi, along with Princess Toadstool and Toad boarded the Ding Bell, which passed the finish line of the river. Mark Twang was last seen being congratulated by Mario, Luigi, Toad and Princess Toadstool for having become King of the River.