One-Hit Kill (God of Destruction) 
European Import: Project Zero
     To kill the God Of Destruction easily, get the Doppleganger card.
Toss it near him and it may kill him with one hit.

     However, the Doppleganger card is difficult to get. You will need
to upgrade the following cards to 9,999 EXP Points:

#45-Great Turtle 
#69-Blue Dragon 
#83-White Tiger* 
#104-God Of Destruction* 

     *  Note:  You will want to copy these cards prior to transforming
because they are rare cards.
 
Unlock Battle Mode, Special Function, Sound Test and Ghost List 
     To  unlock  Battle  Mode,  complete the game once. Also unlocked:
Special Function, Sound Test and Ghost List options.
 
Unlock Chapter Select 
     To unlock a Chapter function, beat the game on Nightmare difficulty.
 
Unlock Nightmare Difficulty 
     To unlock Nightmare difficulty, complete the Battle Mode.
 
Unlock a New Ending 
     To unlock a secondary ending, beat the game on Nightmare difficulty.