SECRET MINE D-1
Welcome to Secret Mine D-1, Cold Case. There are 5 Gem Stones that we recommend grabbing here, as well as one Boo to track down.
Start things off by following the path, up to the cabin, using your vacuum to suck up the snow piles blocking the way. Then head inside the Chalet. After you clear the room of ghosts, proceed through the northeastern door into the Smokehouse. As you approach the obstructed door on the right, the stove will turn on. Approach that to reveal some ghosts. Once clear, use your Dark Light to reveal another towel right next to the striped one. Suck both of them up to reveal a secret compartment containing the mansion's 1st gem.
Afterward, grab one of the burning pieces of coal spat out by the stove and use it to melt the ice blocking the door leading to the Ice Lake. Follow it to the Fishing Hut and use your Dark Light along its southern wall to reveal the entrance. Inside, use your vacuum on the snow pile in the bottom left corner to uncover the mansions' 2nd gem.
Now go ahead and suck up all the snow if you want and work your way to the back wall. Cast your Dark Light onto it to reveal a painting of Toad, and keep shining it to then reveal Toad himself. But all that extra weight will cause both of you to fall through the floor and into the Under the Ice area. Carry Toad to the air vent in the bottom left corner to land on a ledge above.
Now launch Toad into the roped-off area along the northern wall to have him slide through a secret area and knock loose a gem. Go get it by taking the icy slope on the right to obtain the mansion's 3rd gem.
Afterward, take the air vent again and exit through the door into the Terminal. Cross the room and take the door just past the mirror along the northern wall into the High Wires area. Use your vacuum to catch a ride on the wire to reach the far ledge. Once there, use your vacuum to pull the manson's 4th gem from the bird nest.
Now use the Wire to head back into the Terminal, then exit through the door on the left into the Airway. Pick up Toad and launch him into the high lift. His weight will cause it to lower, and another to rise containing a key. Suck up the snow to grab your prize. But before you leave, you might want to take a look through the binoculars, as it's required for one of the gems. Now turn your gaze to the right to watch as a gem is carried by a bat, then dropped into a nearby barrel. Don't worry, you'll be grabbing it soon enough.
For now, head back into the Terminal. Does the room look a little different to you? Such as the sheet covering the mirror--weird! And if you tear it off, you might notice a barrel in the reflection that doesn't seem to exist. Well, use your Dark Light on that spot to reveal the barrel, and this mission's Boo.
Afterward, use your key to unlock the southern door leading into the Prospector's Crossing. Now the Toad here is afraid of the ice, and it will shatter if you attempt to carry him across, so try launching him across first before following behind him. Once you're both across, take the door leading into the Drift Hall. Head right across the ice to find a chest under some snow. Just watch out for some bats that will attack when you start to clear the snow off of it--you'll find a key inside. Now head down the stairs and use it to unlock the door there and gain entry into the Basin. Take down the ghosts that you can see in the floor's reflection, then exit out the left door into the Airway. Here you'll find a bridge that's seen some better days. Use your vacuum on the tassel hanging from its left side to at least raise half of the bridge. Go ahead and cross that half like a tightrope to the other side. Once there, use your vacuum on another tassel, this time on the right, to raise the other half of the bridge, allowing it to finally serve its proper purpose. So go ahead and retrieve Toad and return to the far side. Now if you looked through the binoculars earlier, then you'll want to check the barrel just left of the bridge to find the mansion's 5th gem. Afterward, take the nearby lift back into the chalet. Now just interact with E. Gadd's teleporter along the right wall to return Toad to the lab and complete your mission.