press B before any move is made during a battle.
When you are on the carrier near the end of the game and where you fight Eugene, enter the door with the first-aid symbol (red cross) and search the medicine cabinet for a Naolin Gold. You can search it an infinite number of times and get unlimited Naolin Golds, which you can either use for heals or to sell and get lots of cash.
Complete the game once and thensave it. When you load the saved game, you will start with $300,000.
To save money when you have another character and you get to the final floor, switch to Gre and defeat the Boss. Additionally, Gre has the power to make the Boss wait longer.
At the character selection screen, press X.
If you attack a monster from behind, your characters gets two attacks in a row for surprise element.
When in the carrier go to the 2nd room. You should find 2 doors, one of which leads to a single hallway. You should see a soldier in that hallway. When you finish him off, you can exit to the hallway, and then re-enter to find that he respawns. You can do this inifitely.
