From the Super Mario Wiki
Ads keep the MarioWiki independent and free :)
Super Smash Bros. Ultimate
The Poltergust G-00 was teased in Super Smash Bros. Ultimate's August 8 Nintendo Direct, specifically in Simon Belmont's reveal trailer, where Luigi was shown using its Strobulb, as well as its function to fire toilet plungers. Luigi used the plungers in an attempt to ward off a mummy horde in Dracula Castle, but his efforts failed.
Later in the November 1 Nintendo Direct, the Poltergust G-00 was officially confirmed as a moveset element for Luigi, replacing his previous grab and throws. For his grab, Luigi shoots out a plunger from the Poltergust G-00; as a result, it has much more range than Luigi's previous grab, and it also grants him a grab aerial. Luigi's up throw directly involves the Poltergust G-00, as he uses it to eject opponents at a high upward distance. His forward and back throws were also given new animations to fit his new grab, as he now slams the opponent with the Poltergust G-00 during both these throws. Lastly, his Final Smash now utilizes the Poltergust G-00, with it replacing the Poltergust 5000 function-wise from the previous game.
Luigi's Mansion 3
The Poltergust G-00 debuts in a Mario franchise game with its appearance in Luigi's Mansion 3, being used by Luigi. The Poltergust G-00 uses the Strobulb equipment from previous Luigi's Mansion games, the Dark-Light Device from Luigi's Mansion: Dark Moon, and has the aforementioned ability to fire grabable toilet plungers with the Suction Shot. With the Burst function, the Poltergust G-00 creates a shockwave that can both damage enemies, and allow Luigi to jump with it. Similarly to what it does as Luigi's forward and back throws in Super Smash Bros. Ultimate, the Poltergust G-00 can slam ghosts on the ground or into each other.