From the Super Mario Wiki
Pronto is a native Mushroom who appeared in The Super Mario Bros. Super Show!. He lives in Sudden Death Valley and is gifted with the ability to run swiftly with little effort. Although Pronto is shown to live in a tribe with other native Mushrooms, no other members were ever seen or referenced. Pronto is a spoof of Tonto from The Lone Ranger.
Mario, who had been kicked off his own stagecoach by Billy the Koopa and a Koopa Troopa, found himself stranded in Sudden Death Valley nearly dying of thirst. Pronto overheard Mario's request for water and ran to him. Pronto and Mario introduced each other, and Pronto told Mario that he could tap juice from a cactus if he needed a drink. After Mario quenched his thirst, he informed Pronto that he had to stop Billy the Koopa, who had hijacked the stagecoach he and his friends were using to deliver Gold Coins to Mushridge. Upon hearing this, Pronto realized that Mario would need his help in order to stop Billy the Koopa while in Sudden Death Valley.
Pronto brought Mario back to his tepee, where Mario donned a cowboy suit and a mask. Acknowledging Mario's disguise, Pronto went on to teach him the ways of the west. He presented Mario with a revolver, but when Mario tried to shoot targets with it, his aim was off until he used miniature silver plungers as ammunition. Pronto then tried to teach Mario how to use a lasso, but Mario ended up tangling the two of them until he used a plumber's snake instead of a rope. Mario then managed to tame his Ostro by feeding it a submarine sandwich, and Pronto complimented him on his fast learning. Mario then dubbed himself as the Provolone Ranger, as the two heroes set off to find Billy the Koopa.
After exploring Sudden Death Valley, Pronto got off his Ostro to search for a sign of Billy the Koopa, but came up empty handed. Mario then saw a sign with King Koopa's picture that led into a canyon, and the two of them followed it. Walking into the canyon, Mario and Pronto came to a dead end and walked into Billy the Koopa's trap. Although they were surrounded by Billy the Koopa and his Koopa Troopas, Mario came up with a plan to distract the Koopa Troopas while Pronto snatched all of the Cobrats. Although they were successful, Pronto failed to notice a Pokey, who caught and presented him to two Koopa Troopas, who proceeded to tie him up.
Pronto was taken to the Double Cross Ranch, where Luigi, Princess Toadstool and Toad were also being held as Billy the Koopa's hostages. Tied to a chair, there was little that Mario's friends could do, even as Mario arrived and drove off all the Koopas from the ranch. However, they all cheered him on as best they could.
After Mario scared Billy the Koopa out of Sudden Death Valley, he freed his friends from the Double Cross Ranch and was able to deliver the Gold Coins to Mushridge. There, Mario said farewell to Pronto and proceeded to drive off with his friends on their stagecoach. An elderly citizen of Mushridge asked Pronto who the masked man was, and Pronto responded that he was the Provolone Ranger. The man remarked that they never even got a chance to thank him and invite him to dinner. Mario overheard the mention of dinner and came running back to them at a high speed, stating that he ran faster than Pronto.