Krusty's Fun House (NES)

Unlock All Levels
Hold Up + B + Select on Controller 1 and Start on Controller 2, then turn off the console and turn it back on again. When you start a new game, instead of Level 1 password "HI__KIDS", the password "FLAVE___" will be entered by default. Start a game with this password and instead of scores, the word "CHEAT" will be displayed. All levels from now on are unlocked and free to play.

Once you know this secret password, you can just enter it directly without having to input this entire cheat.

When you enter this password, an internal flag is toggled on and off, so if you enter it one more time before powering down the console, the cheat mode is disabled, and the password will just be treated as a Level 5 password with all levels completed instead.

Easter Egg
Enter the password "GSSMELLS" to change all in-game enemies into the huge mice that normally only appear at the "Game Over" or "Hi Kids" screens at the end or start of the game.

Unused Text
One more secret password exists: "GLPLONKA", which is never used and has no disabled code assigned to it. Its original effect is unknown.

Additionally, the reset routine uses the string "GAZ" to check if game was soft or hard reset.