Stand in front of any mirror in the mansion except for the large one that reflects the invisible ghosts. Then, switch to your Game Boy Horror's first person mode and press A to warp to the entrance hall of Luigi's Mansion.
Successfully complete the game and save. Ura-Yashiki (Another Mansion) mode will now be available to the main menu. This mode allows you to play the game with various differences. You can get a different sized house at the end of the game, depending on your rank.
Successfully complete the game to unlock everything in the gallery.
Use your vacuum to clean all lamps, chandelier, and vases, as most contain either hearts and money.
While playing the game, hold B + X press Start for about two seconds.
At the map screen, press A to zoom in. Then, use the C-stick to scroll around the floor that you are on.
To obtain an "A" rank, get all the gold mice, catch all the blue ghosts, get both gold diamonds, and collect as much money as possible. You need $100,000,000 to get an "A".
There are three different medals you can collect to change the powers of the Poltergust 3000 vacuum cleaner. They are the Fire, Ice, and Water medals. When you collect the Fire Medal, you can suck up ghosts that have a ring of fire around the health hearts. Also, you can press L to spray fire from your vacuum to light candles and hit ghosts with a ice health meter. When you collect the Water Medal, you can extinguish flames that are too powerful for your vacuum to put out. Also, you can press L to spray water.
When you press A, Luigi will call "Mario!". The more damage Luigi has taken, the more desperate his call for Mario will be.
Although you cannot pull off the projection room screen, you can make it change. Give it a tug with the Poltergust 3000. If you are persistent, you will reveal a huge picture of a Boo. There is another hidden Boo picture in the first floor bathroom. Vacuum at the poster with the word "Monster" on it. A picture of a Boo will appear.
First floor graveyard: When you interact with the leftmost gravestone as well as others, you will collect a big heart.
Second floor nursery: The design of the heart-shaped dresser is a clue. Open the drawer to find a 50-point heart.
Third floor safari room: Your first destination on the third floor is a difficult room. Its big heart is in a chest on a corner table.
Basement cellar: The shelves in the center of the cellar hold a big heart. Pull it out with your vacuum.
First gold diamond: Given to you when you catch Boo number 50.
Second gold diamond: After you fight the dog outside the mansion, water the seed under the balcony. It will sprout. Return after going to the next area, water it again, and it will grow again. Return again after beating the Giant Boo on the balcony, and water it again. It will spit out a lot of bills, coins, and finally a gold diamond.