There are six collectible gems on each floor in Luigi’s Mansion 3. In this guide, I’ll show you where to find all six gems on the 3F floor and tell you how to get your hands on them. You’ll need to unlock certain abilities before you’ll be able to collect some of these gems, so you may have to come back later on in the game.
Please note that some of the gems will appear clear rather than coloured in the screenshots seen below, this is because I had already collected them during my playthrough before creating this guide.
Gem #1 – Restroom
As soon as you exit the elevator, head to the right and into the far Restroom. Once inside, look in the mirror in the upper left corner of the room and you’ll notice that there is a grate in the floor in the reflection, but it doesn’t appear to be on the actual floor of the room. Shine your Dark Light on the spot on the floor where the grate appears in the reflection and the grate will slowly appear. Now use Gooigi to slip through the grate, run to the left underneath the second Restroom, and blow air at the valve to shut off the water supply to the Restroom above. This will stop the toilet above from overflowing, which means Gooigi can now get across the room to get to the Purple Gem, which you should be able to see in the left-hand cubicle – all you have to do now is get in there! Take control of Luigi again and use a Suction Shot on the vent cover next to the mirror, exposing another grate which Gooigi can slip through. Take control of Gooigi to slip through the grate into the next restroom and grab your prize.
Gem #2 – Boutique
Now head back towards the elevator and through the revolving door on the left. As soon as you get through the door you’ll see the Boutique right next to you, but there’s a closed gate across the entrance. Take control of Gooigi and slip through the gate, then perform a Suction Shot on the mannequin on the left-hand wall of the room to open a secret door just next to it. Head through the door into a small secret room which contains a chest, and you’ll see the Red Gem sat on the beam above it. Use your vacuum to get your hands on it.
Gem #3 – Accessories
Head up the escalators and turn left at the top. You’ll see the Accessories shop, which also has a closed gate blocking the entrance. Slip through the gate with Gooigi, then use a Suction Shot on the big case in the centre of room. Drag it towards the big glass cabinet at the back of the room, then swing the case into the cabinet to smash it and release the Yellow Gem.
Gem #4 – Mall Lobby
Shine your Dark Light at the left-front window of Accessories and a ladder will appear. Climb it and follow the balcony all the way to the right where you’ll find a chest which contains the Green Gem.
Gem #5 – Elevator Hall
Run back across the top of the escalators and then run towards the camera. You’ll come to a small broken gate which is blocking your way, which you can open by using a Burst. Once opened, follow the pathway all the way to the right, around the top of the elevator, and into a small secret room which houses a chest which holds a whole bunch of coinage and the Clear Gem.
Gem #6 – Hallway
Head to the right in the upstairs area as if you were heading towards the Security Office, but stop at the vending machine outside. Use your Strobulb on it over and over: you’ll get bills, gold bars, and a whole bunch of rats, but just keep going and eventually it’ll spit out the Blue Gem.
And that’s it! Congratulations, you collected all six gems.