From the Super Mario Wiki
The Plumbinator was a Robo Suit which resembled a plumber that was built out of spare parts by Dr. Nerdnick and Bunsen for Mario and Luigi so that they could fight Robo Koopa. The Plumbinator required both Mario and Luigi to operate it, with Mario controlling the suit's upper half, while Luigi manned the lower half. Not too much is revealed about the Plumbinator, but it appears to have been less dangerous and powerful than Robo Koopa's suit.
Unable to fight off Robo Koopa, Mario, Luigi, Dr. Nerdnick and Bunsen retreated to a junkyard in Robo Land, where Dr. Nerdnick concluded that the only way Mario and Luigi could face Robo Koopa was with a robo suit of their own. Having limited access to parts and tools, Dr. Nerdnick improvised and constructed a robo suit from whatever he and Bunsen could find around the junkyard. Although Mario and Luigi had trouble keeping the Plumbinator's under control at first, they went off to face Robo Koopa.
As Robo Koopa fought the Plumbinator, Mario and Luigi did what they could to fend off against his powerful attacks. They deflected his Bomb Plants with their fly swatter, and dodged whatever he could hit them with. Mario tried to blast Robo Koopa with several eggs, but they proved to be useless. Robo Koopa managed to wrangle the Plumbinator with a lasso, but Luigi cut it with a pair of scissors. The Plumbinator tried to escape Robo Koopa by leaping on top of a rooftop, but Robo Koopa followed. Robo Koopa soon caught up with the Plumbinator and kicked it off of a building, causing it to fall onto a walkway and break into several pieces, ultimately destroying it.
The Plumbinator only had three known abilites. It could extend a telescope from within its buckle, giving Mario enchanced vision capabilites. It could also extend a fly swatter from its buckle, which was intended for deflecting attacks. Lastly, it was capable of launching eggs from a tube that was built into the helmet, although what purpose this function was intended for is unclear, as the eggs did little to stop Robo Koopa.