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 was given to Mario in a flashback sequence by the President for saving him and Mikhail Gorbachev from a flooded street in Brooklyn.
Mario lost the Golden Plumber's Helper in a fight with King Koopa, as he accidentally got it stuck onto the tyrant's nose in the process. When Mario and his friends were trapped at the bottom of a hole, Mario worried that he would 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 managed to get the Golden Plumber's Helper off of Koopa's nose, and Mario was finally reunited with it.
Despite the Golden Plumber's Helper's importance to Mario, it was never seen in any other episode. Presumably Mario secured the Golden Plumber's Helper in the Princess' castle or back in Brooklyn in order to prevent it from ever falling into Bowser's hands again.