Bigger Hearts
Collect as much money as possible. The more you collect, the bigger the hearts you will get. They almost restore as much hearts as big hearts can.
Boo types
There are 4 types of boo's, red, blue, white, and black with an outline.
Extra money
Check all lamps, vases, chandlers, and cuboards.
In-game reset
Hold B and X and press start for about 2 seconds.
mario calls
When you press @, luigi calls mario's name. The more health he has lost, the more scared he sounds.
Move map
Press @ on the map screen to zoom in. Then use the C-stick to move around the floor you are on.
Pokemon Painting
On level 2, go to the 1st bathroom to find a painting of pokemon.