From the Super Mario Wiki
The Power Shower was a system of pipes and shower heads that was designed by Kooky von Koopa which was utilized to create an artificial rainstorm in the Mushroom Kingdom. The top of the Power Shower was situated above the Mushroom Kingdom, and was supplied water through a long pipe that extended from underground.
In The Adventures of Super Mario Bros. 3 episode "Oh, Brother!", Kooky had 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 traveled through the Pipe Maze, flushing out all the loose Gold Coins, and washed them into a basin in one of Bowser's dungeons.
When a pipe in the dungeon that supplied water to the Power Shower had burst, Bowser ordered Kooky to fetch Mario so that he could fix it. After Kooky caught Mario with his Plumber Pole, he used his Lame Brainer to make Mario their mindless slave. With Mario under the Koopas' control, he fixed the leak in the Power Shower.
After Luigi saved Mario, the two of them managed to dismantle the Power Shower, and it was never seen again.
 Names in Other Languages