Enter any of the following for your password:
FIRST POWER-UP &1#1#
SECOND POWER-UP ?1S1M
THIRD POWER-UP BLSRS
GAME ENDING #Z6D?
To get 4 free lives each time your game is over, walk past the continue door to the left and there is a room where you can collect them.
In the hall of rooms, walk left until there is a door above you. Push up to enter a secret room; collect all the stuff in this room and go directly above where you entered this room and press up to enter the other secret room.
On some versions of the game enter the code `11111’ on the password screen for 100 lives. 
For Morticia, use the 3rd power-up code, go to the piano room and wait for the Addams Family music to play. Now open the self sealed door and finish the last level.
Pause the game by pressing ‘SPACE’ and then hit the ‘ESC’ key. You will now be in a room with a continue door and an escape door. Instead of choosing one of these options just keep walking left until you come across another room full of extra lives.
 This cheat doesn't work with the SPS release 0419.