From the Super Mario Wiki
Lightplungers are space-age weapons that only ever appeared in The Super Mario Bros. Super Show! episode "Star Koopa". Despite their name, Lightplungers deviate from the appearance of standard toilet plungers greatly, though their hilts do somewhat resemble plungers.
When not in use, Lightplungers resemble little more than a metal handle. Upon activating a Lightplunger, a javelin-shaped energy beam will extend from the handle, which is capable of paralyzing anyone it touches.
In "Star Koopa / Santa Claus Is Coming to Flatbush", Mario, Luigi, Princess Toadstool and Toad resorted to using Lightplungers to fight off the attacking Stormtroopas, who fought with Lightplungers of their own. As they dueled, the Stormtroopas showed to be unsuccessful in fighting with Lightplungers, and the entire pack was defeated after they were all shocked with their opponents' Lightplungers.
Darth Koopa then appeared to avenge the defeat of his Stormtroopas, and was challenged into an intense Lightplunger duel by Mario. Although neither of them were ever hit with a Lightplunger, Mario managed to kick Darth Koopa against a wall, where he had him pinned down with his Lightplunger. However, before Mario could triumph, Darth Koopa froze him, along with the rest of his friends, with his Freeze Gun.