Getting stuff early
You can get items from Farther earlier in the game. First put in the invincibility code and go to the world map. Because of a flaw with the code use controller two and push left or right to choose where you want to go. you could actually select a game that you are only about a half an hour into, and go to Ballacetine castle and get the battle shield!
Invincibility
Begin and save a game, then press RESET and wait for the American Sammy logo to and fully appear. Now press UP, DOWN, UP, DOWN, SELECT, START on controller 2 before the logo disappears. Select Continue and then press SELECT to bring up a sub-screen. Now, press START on Controller 2 and the word "Debug" will appear next to Status if you've done this correctly.
Sound Test
While playing, press SELECT to bring up a subscreen, then hit START on Controller 2.