Golden Plumber's Helper
From the Super Mario Wiki
The Golden Plumber's Helper is a toilet plunger that is apparently made of gold, which was seen in The Super Mario Bros. Super Show! episode "Plummers Academy". It is given to Mario in a flashback sequence by the President for saving him and Mikhail Gorbachev from a flooded street in Brooklyn.
Mario loses the Golden Plumber's Helper in a fight with King Koopa, as he accidentally gets it stuck onto his nose in the process. When Mario and his friends are trapped at the bottom of a hole, Mario worries that he will never get the Golden Plunger back, and tells the story of how he earned it to Princess Toadstool and Toad.
After escaping from the hole, Mario and his friends manage to get the Golden Plumber's Helper off of Koopa's nose, and Mario finally recaptures it.
Despite the Golden Plumber's Helper's importance to Mario, it is never seen in any other episode. Presumably Mario secured it in a place like Peach's Castle so that it would never accidentally be lost to Koopa again.