Monster Seed/Cheat codes

Buy any monster
Go to the Soulin Fighting Monster, Item Store and talk to the shop owner. This will bring up the main shop menu. Enter psx: R2, psx: R1, psx: L2, psx: L1, psx: R1, psx: R2, psx: L1, psx: L2, psx: L2. Once entered the game will beep three times and now you can buy any monster, even enemy NPCs. When you exit the menu the code will no longer be in effect and the store's stock of monsters will revert back to normal.

Watch the ending movie
At the title screen enter psx: L2, psx: R1, psx: L1, psx: R2, psx: L2, psx: R1, psx: L1, psx: R2, psx: R2. Once entered the game will beep three times and ending will be added to the bottom of the list of options on the main menu.