Select level
Press "L" at the main menu.

Secret poem
Press "X" at the main menu.

Display development team recommendations
Hold [Option] and click on the "Double Trouble" title.

Display human rights abusers
Hold [Option] + [Command] and click on the "Double Trouble" title.

Hidden message
Hold [Option] and click on the Information bar.

Hidden startup message
Set the Macintosh system date to October 31, 1996 and load game.
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Extra lives
Pause the game and type "extra". (The maximum number of lives you may receive is 8.

Become invisible
Pause the game and type "invis".

Trap opponent inside a bubble
Pause the game and type "catch". (You will trap your opponents within a bubble for roughly eight seconds and then they will escape.)

9,000 points
Pause the game and type "score". (Note: Activating cheat will disable high scores.)