Elevator Hall (Boilerworks)
From the Super Mario Wiki, the Mario encyclopedia
When Luigi initially visits the Elevator Hall, he runs into Clem, and accidentally awakens him by stepping on a rubber ducky. Clem then pranks Luigi by turning a nearby valve to spray Luigi with water before escaping into the next room. Luigi must then use the Poltergust G-00 to turn back the valve and thus turn off the water, then pull off a sheet to the right of a pipe entrance to reveal another pipe. Gooigi must then travel through said pipe entrance to grab a key which Luigi can use to access the Waterworks. Luigi eventually returns here to look for a Toad searching for the Super Suction component, where he is forced to fight a Possessed Bin to advance to the Waterworks.
The yellow gem is found to the left of where the key is found, and simply requires Gooigi to vacuum up some obstructing cobwebs to collect it. Additionally, the Dark-Light Device can reveal a ladder near the elevator doors that leads to a high beam, which in turn leads to a treasure chest containing Coins, Bills, Gold Bars, and a Pearl.
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