Unlimited time:
Enter the following password.

Level skip:
Enter the following password, then pause game play and press Select to advance to the next level.

Unlimited lives:
Enter the following password.

Unlimited energy:
Enter the following password.

Negative mode:
Enter the following password.

Different endings:
The game will display three different endings depending on the number of script pages that are obtained (less than 10, more than 10, or all 24).

Password notes:
The password system is based on the following characters (in order):

Y = Yakko
W = Wakko
D = Dot
R = Ralph (guard)
P = Pinky
B = Brain
N = Nurse
C = The CEO.

When "adding" to a password character, move down the list the indicated number of characters. For example, the notation Y + 2 changes Yakko to Dot. Start again at the top of the list if "adding" to a password character moves off the bottom of the list. For example, the notation N + 3 changes the Nurse to Wakko.

The password is in a grid format where each position is indicated by the following:

A1, B1, C1, D1
A2, B2, C2, D2
A3, B3, C3, D3
All levels and all script pages:
Enter CYWD RPBN CYYR as a password.

Custom passwords:
Create an empty base password by starting a game and dying without doing anything. One of eight base passwords will be displayed. Edit this password, following the guidelines described in the Password Notes section:

Stage completion
Intro: B1+1
Aquatic: A1+1
Fantasy: B1+4
Sci-Fi: B1+2 Adventure: A1+2
Pinky/Brain: A1+4
Script pages
Aquatic: C2+2, C2+4, B2+2, B2+4, B2+1, C2+1
Fantasy: A2+4, A2+2, D1+1, A2+1
Sci-Fi : D1+2, C1+1, D1+4, C1+2, C1+4
Adventure: A3+1, A3+2, A3+4, D2+4, D2+1, D2+2
Pinky/Brain: B3+2, B3+4, B3+1

Perfect ending
Start from the base code, subtract 1 from all characters except C3 and D3, add 2 to C3.

Bonus coins:
Locate the large plant near the CEO at the start of the game. Push it to the right. It will explode when it touches the CEO and reveal a door. Enter the door to reach a secret room filled with coins. Note: This trick only works once.