Cheats:

Unlock options in extra option menu:
     Every  time  basic mode is completed with a different character a
new option will be unlocked, until the extra option menu is full.

Play as Pride:
     Successfully complete basic mode with seven different characters.
He looks like an old Fokker, but has different moves.

Play as Mel:
     Successfully complete basic mode with eight different characters.
She is the girl from shop mode and fights similarly to Julia.

Extra Arenas:
     Successfully  complete  basic mode with all characters, including
Mel  and  Pride to unlock three new arenas exclusive to original mode.
To  access them, move the pointer left or right at the arena selection
screen  until  it  is  off-screen.  A large box with the "Extra Arena"
message  will appear. Select the desired extra arena. The arenas are a
small  room,  a  very  narrow  bridge over along drop, and a geometric
(cubes stacked in weird patterns) arena.

100,000 credits for shop mode:
     If during the course of the game you manage to pick up item #103,
which  resembles  a  red  turban,  sell it for 100,000 credits in shop
mode. This item seems to appear randomly.

Full pause screen:
     Pause the game and press X + Y.

Getting EVERYTHING in the shop mode:
     At  the beginning of the game where the logo Power Stone 2 starts
to  appear,  quickly  repeated  press  Start, X, Y, X, Y, Start, X, X,
Start  and  when  you  hear a sound of a bird chirping, that means you
have recieved all of the items in the shop window.

Using the super form forever:
     Kill  one  enemy  with  only  one  button  punches, and when that
character  dies,  you will automaticly charg up, its like having the 3
power stone forever.