Press the [Enter] key during play, and an input field appears. 
Then input the following cheat codes:

Icompletedthisghostgame - Carries you into the unreal world.
IfIwantIgotit 32 - Gives you items. The number at the end is the number 
of the item you want.
Seethesilverlining - Remove the darkness.
Showmetheworld - The whole card releases, and displays also the positions 
of the opponents, who disappear to darkness.
Thefierceunknownpower 99 - Increases Magic to 99
Thegreathealthpower 99 - Increases Health to 99
Thehealthyspiritpower 99 - Increases Brain to 99 
Theoriginaldexteritypower 99 - Increases Dexterity to 99 
Therealmusclepower 99 - Increases Strength to 99 
ThesoulHunter'sholyPower 10 - Increases power to 99 
Youcansaymoneyiseverything 10000 - Gives you bucks. 
Yougainasoneplease 30 - Gives weapons. The number at the end is the number of the weapon that you want. 
The cheats are case sensitive, and must be entered exactly as shown.