Luigi's Mansion 3 6th Floor gems
In the Royal Coffers
Walking along the hallway before the arena you'll be able to vacuum a tapestry off the wall and use your dark light to reveal a door. Walk inside to find gold and a gem.
In a suite of armor on the balcony
Once you've taken the boss out, head to the exit that connects you with the route back to the elevator. There will be a suit of armor propped up, the one on the left has a gem.
Hall with multiple armor sets
Use your dark light to reveal a set of armor in the alcove that's empty. Use your plunger on it afterwards and you'll get a gem.
The Wine Cellar
The rightmost barrel contains a gem, open it and then go right and climb up to collect the gem.
Armory
Use your plunger to open up the bricks in the center of the room with weapons, the wall should collapse revealing a chest that contains a gem.
In the Cage
Use Luigi to blast the propellor in the room with the manual elevator, that will lower a cage that contains a gem. Use Gooigi to grab it.
Luigi's mansion 3 7th Floor gems
On the very top of the plant through a hidden passageway
Use your your vacuum to pull the plant on the far end of the room towards you, then walk behind the glass over to a hidden gem.
Watermelon Bathroom
Use your dark light to reveal a pipe by the toilet. Head down with Gooigi and use the dark light again to reveal a missing section of piping. Switch back to gooigi to turn the faucet in the bathtub and a gem should pop out for Gooigi to grab.
Hidden in the nightstand
In the room with a ton of yet-to-bloom flowers, use your plunger to open up the night stand in the corner. Use Gooigi to go through the pipe and hit the flower with a burst of light. A gem will pop out.
Underneath the mushroom room
Follow the path of the vines on the ground, they will lead you underground. Use the pipe in the underground to reach the blocked off area and find a gem.
Petal bathroom
In the bathroom covered in flower petals, a gem will be revealed in the bathtub after you vacuum up the petals. Keep clearing the petals until you find a pipe, follow it with Gooigi and go underground. Use the other pipe there to get into the bathtub and grab the gem.
In the hall near the elevator
Use your dark light to reveal a gem that's attached to a plant.
Luigi's Mansion 3 8th floor gems
Under the carpet, before you enter the studio
Use the vacuum to pull the carpet back and a gem will pop out.
Inside the giant film award
Just pull the knob on the reel in front of it and a gem will pop out, use Gooigi to pick the gem up.
On top of the catwalk
Climb onto the lift in the corner of the main room with Luigi, then use Gooigi's vacuum to turn the crank and lift him up. The gem will be trapped in ice, then go through the TV sets, which is a feature on this floor, onto the fire set.
Throw the ice block onto the set and use Luigi to turn the camera on. Then grab the Ice Block with Gooigi when your on screen and melt the ice with the fire from the set.
Fire Set
Pull the cloth off the bike on the fire set and a gem ghost will pop out. Catch it and collect the gem.
Toy Story set
Use Gooigi to slip into the bottle next to the giant box on the set full of huge objects. A gem is inside.
Next to the Elevator
Use your vacuum on the helicopter just outside the elevator and a gem will pop out.
Luigi's Mansion 3 9th Floor gems
Smash the Pterodactyl
Grab the vertebrae bone from when you fight the boss, carry it towards the elevator and shoot the flying beast down. A gem will pop out.
Smash the glass case
Most of the gems on this floor require you to smash something open. Use the same bones from the T-Rex to smash the box case in the right corner. A gem ghost will pop out. Catch him and collect the gem.
Spin the desk chair
Spin the swivel chair continuously with a stream of air and the whole desk with flip into the ground and a chest with a gem will pop out.
Light hidden behind a plant
There will be a blinking light covered by a plant in the hallway on the left hand side of the floor. Use your vacuum to remove the plant, flash your light to reveal a gem.
Smash another case
Smash the case on the left hand corner of the room and use your dark light to reveal a hidden gem.
Smash a final case
Use the bone from the T-Rex to smash the case next to the entryway to the main hall.
Luigi's Mansion 3 Boiler Room gems
Hidden in Paint
In the old reservoir room you'll see a paint can on the bottom level. Grab the paint can and throw it at the wall. It'll reveal a ghost gem, catch it and collect the gem.
Storage Room
Use Gooigi to enter a pipe behind the mop/bucket, use Luigi to turn the valve near the entrance. Have Gooigi go through the other pipe on the left side of the room, use Luigi again and turn the same valve back. This should let Gooigi collect the Gem underneath the floor.
Observation Deck
Use the dark light to reveal a water container in the back corner of the room, then use your light to activate the flashing light on the control unit. A gem will pop out from the vent that's next to it.
In the Sewer
Once the Sewer is drained after you beat the floor head back to the middle section of the walkway. Use Luigi to pull the chain next to the lift and grab the gem hanging by the chain.
In the hidden submarine
Use your plunger on the periscope that's sticking out of the ground in the third section of the sewer. Use Gooigi to go down it. Grab the canister to the stove to reveal a gem.
Elevator Room
Use Luigi's vacuum to reveal a fake brick wall and then use Gooigi to go into the pipe behind it. This will lead you to the scaffolding higher up, head backwards to the left and follow that passageway to a gem.
