Luigi and the Haunted Mansion is the first level in the Ghostly Galaxy. The Ghostly Galaxy is found in the Kitchen dome.
You’ll start off the level on a Toad spaceship. On the bottom side of the spaceship is a Launch Star that will take you to the mansion’s grounds. When you reach the grounds you’ll find lots of Pumpkinhead Goombas. The pumpkins act as armor, you can spin attack it off and reveal the goombas who you can then defeat like normal.
When you’re ready, head across the path towards the Haunted Mansion. Make sure you watch out for the Chain Chomp rolling down the path!
When you’re inside, a Boo will spawn. You can only defeat them by shining a light on them. To the right of the Mansion entrance, you’ll find a switch that turns on a spotlight. Use Y to spin the Boo into the spotlight. Another Boo will spawn as you walk up the steps. He holds a key that you need to obtain to progress through the level. Spin the second Boo into the spotlight to reveal the key and open up a door at the back of the room.
Collect the Star Launcher Chips
In the new room, you’ll need to collect the five Star Launcher Chips. There are a few Pumpkinhead Goombas around the room and you’ll also need to use the bridges to move from the floor to the walls and then to the ceilings to reach all the chips.
When you have all the chips, a Star Launcher will spawn in the window on the right wall. This will take you to a higher area of the Haunted Mansion.
When you arrive on the new platform, you’ll find three Pull Stars to help you grab the door key. You’ll need to jump down into the key then quickly pull yourself to either of the Pull Stars. When you’ve got the key you’ll open up a new corridor in the Mansion.
When you enter the new corridor, there are a couple more Boos that you’ll need to spin into the spotlight. In the far left corner of the room at the end of the corridor, you’ll find a Boo Mushroom, that will transform Mario into Boo Mario.
Boo Mario can fly by pressing A/B and can also go invisible and float through walls by using Y or by shaking the Right Joy-con. If you go into a spotlight you will transform back into normal Mario, though.
Use your invisible power to pass through the fencing wall to get to the final room.
In this room, you’ll need to use the invisible power to move through the other fencing wall and then let the spotlight in the small room revert your form back to normal Mario. Use the spring jump to jump over the bookcase to the room where you’ll find Luigi.
Speak to Luigi and he will give you a Power Star. After this level, Luigi can be found at the Toad’s Garage at the Observatory.