A-4: Visual Tricks
Luigi has to go to the Lab in order to retrieve the Dark-Light Device. When Luigi arrives at the door, however, it disappears due to the presence of Spirit Balls. Luigi has to find another way to access the Lab; he should go upstairs to find a way down. If Luigi goes up the stairs, however, the room turns dark and the stairs slide him down to the bottom, similar to what happens in A-2: Gear Up. This time, a Hider and a Slammer appear. Once the Hider has been defeated, two more appear. As soon as all ghosts get defeated, the room lightens up and Luigi has access to the second floor.
Luigi should then go into the Parlor. As he enters the room, the fire in the fireplace goes out, enabling Luigi to use it to access the Lab. In the Lab, Luigi sees the Dark-Light Device; as soon as he is about to take it, however, a Greenie with sunglasses appears and takes the Dark-Light Device, and it hides in the blackboard. Just as in A-2: Gear Up, Luigi should suck the blackboard, flipping the ghost until it is thrown out. In order to defeat this Greenie, Luigi should suck up the sunglasses, then use the Strobulb on it to suck it in. After this Greenie is defeated, two more wearing sunglasses appear. Defeating the rest of the Greenies reveals the Dark-Light Device.
After Luigi acquires the Dark-Light Device, he should use it on the hidden door, causing Spirit Balls to fly out of it. Luigi should suck all of them in in order to reveal the door. This applies to all hidden objects later in the game. Luigi should then go up the Common Hall and use the Dark-Light Device on a painting with a key in it; doing this releases the key from the painting. After this, Luigi should use the Dark-Light Device on the hidden door to access the Patio. In the Patio, Luigi has to find a hidden statue to the right of the fountain. After using the Dark-Light Device to reveal the statue, Luigi should rotate the fan with the Poltergust 5000, causing the statue to reveal a key. This key allows access to the Kitchen. The Kitchen is dark; there are four Greenies and two Hiders in this room. Once Luigi defeats them, he can access the elevator on the right, revealed after Luigi pulls a cord. This elevator takes him to the Dining Room.
In the Dining Room, it is dark, and Luigi can see a Boo releasing Spirit Balls that hide objects. After Luigi uses the Dark-Light Device on the Dining Room table, the Boo finds out that the hidden objects are visible again and gets furious at Luigi for revealing them. Luigi should use the Dark-Light Device on the Boo to reveal its location, and then he should pull its tongue to send it bouncing around the room, making it lose HP. Once it is out of HP, Luigi can suck it in. Luigi then can return to the Bunker when this is accomplished.
Criminy! Someone's been casting illusions in the Gloomy Manor! We'll need my Dark-Light Device to see through this hooey. I'm pretty sure I left it in the Lab.