Deadly Towers

Battle with Rubas:
Enter EF1KDK.KTX, 54DK1P4WC, or .AZODKNXTJ as a password.
Information in this section was contributed by bking.

Extra items:
Enter FE1K10.TDK as a password.

Enter GDXHDPMM10 as a password to start with all attack and defense items, Hyper Boots, and 5 Bells.
Information in this section was contributed by mixup2001111.

300 maximum HP:
Enter O51O1MYILJ as a password.

Enter O51O1MNOLB as a password to start with the Normal Sword and a maximum 300 HP.

Super passwords:
Intentionally die immediately after starting a new game. Change the first two letters of the password displayed to "EF" or "FE", then re-enter the revised password. Your character will have 102 hit points when game play resumes.

Enter FEZN3I6P.Q as a password for 222 hit points, all the armor, and six out of seven Bells.
Information in this section was contributed by Levi.

Enter EE1KBK.TTT as a password for the best attack and defense items, 50 Ludder, the magic key, have Rubas' lair unlocked, have all seven towers accessible, the enemies and shops at beginning level, and 86 maximum HP.

Hint: Upgrades:
In towers, or on your way up to the entrance of towers, walk up and down each floor, and in the corners of each room. Most towers have a secret room with a upgrade sword/shield or a figurine, and some have a secret "parallel" version of the tower, where you must look around for an upgrade and search for the exit.
Information in this section was contributed by Chris Hardewig.