From the Super Mario Wiki
The Power Shower is a system of pipes and shower heads that is designed by Kooky von Koopa which is used to create an artificial rainstorm in the Mushroom Kingdom. The top of the Power Shower is situated above the Mushroom Kingdom and is supplied water through a long pipe that extended from underground.
In The Adventures of Super Mario Bros. 3 episode "Oh, Brother!", Kooky has activated the Power Shower two weeks prior to the events of the episode, forcing rain to pour through the Mushroom Kingdom and down through a Warp Pipe leading to the Pipe Maze. The water then travels through the Pipe Maze, flushing out all the loose Gold Coins and washes them into a basin in one of Bowser's dungeons.
When a pipe in the dungeon that supplies water to the Power Shower has burst, Bowser ordered Kooky to fetch Mario so that he can fix it. After Kooky catches Mario with his Plumber Pole, he uses his Lame Brainer to make Mario their mindless slave. With Mario under the Koopas' control, he fixes the leak in the Power Shower.
After Luigi saves Mario, the two of them managed to dismantle the Power Shower, and it is never seen again.
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