Luigis Mansion

Warp to main entrance hall
Stand in front of any mirror in the mansion then, change to your Game
Boy Horror's first person mode and hit the A button to teleport to
the entrance of Luigi's Mansion. Note: This work with any mirror
except for the large one that reflects the invisible spirits.

Desperate Mario calls
Hit the A button to call "Mario!".

Reach "A" rating:
Catch all the blue spirits, collect all the gold mice, find both of the
gold diamonds and reach at least 100,000,000.

In-game reset
Hold B + X and tap Start buttons for about two seconds during game play.

Find bonus money or hearts
Clean all lamps, chandelier, and vases with your vacumm cleaner to find
bonus money or hearts.

Unlock all gallery mode items:
Finish the game once

Play in Another Mansion mode - Ura-Yashiki
Finish the game once then save.

Map
Hit A button to zoom at the map screen.
Use the C-stick to scroll around the stage.

Mario item locations
Courtyard: Letter
Laundry Room: Cap
Observatory : Star
Projection Room: Glove
The Twins' Room: Shoe

Big heart locations:
1st floor graveyard
2nd floor nursery
3rd floor safari room
Basement cellar

Gold mice locations
Kitchen: Dining Room
Main Hall on first floor: The Study
Main Hall on second Floor: Madame Clairvoya
Random: With Cheese
Sealed Room : Safari Room
Tea Room: Tea Room

Blue Ghost locations
Go to the Billiards room. Look under far right table
Go to the Breaker room. Look under table at left
Go to the Cellar. Look in to the boxes at left of door
Go to the Dining room. Look in to the closet at left
Go to the Kitchen. Look in to the oven at left
Go to the Nana's room. Look under far right chair
Go to the Recreation room. Look in to the machine at bottom right
Go to the Sealed room. Look in - to the chest at far right
Go to the Storage room. Look in chair at right
Go to the Study. Look behind desk in the chair
Go to the Wardrobe room. Look in to the chest on right