Start your game, doesn't matter how many players. When you have the option of selecting your character or entering a password, at least one of the players should choose password. Enter "HOMINGAAA" and press Button 1. It will say "Password Error", but don't worry, just press Button 2 to go back and this time choose your character. Now, whenever you attack, hold the button and press the directional pad to make your weapon go anywhere on the screen.
To see the secret ending for Dungeon Explorer, you must input the invincibility code so you can pass through objects. When you take the ORA stone back to the King and he leaves, you can then pass through the blockade to his throne, which will initiate the secret ending.
To use the Harmit (bad spelling in games, gotta love it). level a Bard until you have at least 50 HP. Go into the second house to the west of Axis Castle. You will be transformed into the Hermit.