In-game reset:
While playing, hold B + X and press Start.
Rubies & Gold:
Water plants to get hidden rubies or gold.
Golden Mice:
Search the floor for hidden pieces of gold cheese...once you find these a gold mouse will appear. It is impossible to get a rank of A upon completion of the games without collecting these mice. Once the lights come on you will not be able to get them and the cheese will dissapear. However in the ending stages of the game the lights will go out again and you will have another chance to get the mice again.
Hidden rooms:
There are two hidden rooms in the mansion also. The first of these rooms is accesible by peering into a mouse hole on the first floor, in the room where the candle holding butler was detained. The second of these rooms can be entered by simply falling down the hole on top of the right tower situated on the very roof top.
Secret Key:
There is a secret key available to make travel around the mansion easier...it is located in the gym attatched to the court yard and can be found by simply peddling on the tred-mil for a while.
Hint:
When you are near a mirror, get out your "Gameboy Horrer" (X) and take a picture (A). This should take you directly to the start.
(supplied by: lawegdi)
Easy hearts:
When you enter the mansion go to baby chancy's room. You will see a chest of drawers with a picture of baby chancy on it. Hit it or vacuom it or somthing and it will give you a medium sized love heart(life energy). This will continue for ever, but to get it to keep giving you love hearts, you have to go to area 2 and come back( this cheat only works if you have defeated baby chancy).
(supplied by: lawegdi)
Move map:
At the map screen, press A to zoom in. Then, use the C-stick to scroll around the floor that you are on.
(supplied by: Ciscotv)