Dynamite Dux

The Amiga and Atari ST versions of Dynamite Dux feature an alternate intro sequence that is checked when the game runs the title screen. If a secret code word is entered into a specific memory location, the intro sequence text changes. The original text spread over 4 screens is:

One day, Lucy was playing with her pets Bin and Pin in a beautiful flower garden.
Then suddenly an evil black shadow appeared and changed into Achacha the great while they were watching.
Lucy startled and frightened was kept in a miracle ball and taken away to Achacha world by Achacha the great.
Therefore Bin and Pin rose up and ventured into Achacha world to rescue her.

If you overwrite 5 bytes with the word DIRTY, when you start the game the intro sequence will now say:

One day, Lucy was playing with herself, while Bin and Pin were buggering each other in the beautiful flower garden. 
Then suddenly an evil black pimp appeared and changed into some kinky leather gear while they were watching. 
Lucy startled and orgasmed at the size of his miracle balls, and disappeared with the pimp to his sleezy brothel. 
Therefore Bin and Pin stopped giving each other one and ventured into the brothel, not wanting to miss out.

Alternate Intro Detection

At address $1e20a in memory is the following ASCII text:

IF YOU WANT TO SEE SOMETHING DIRTY PUT CODE HERE >>>>.....

To activate the alternate intro, overwrite the 5 full stops at address $1e23f with the word "DIRTY" like so:

IF YOU WANT TO SEE SOMETHING DIRTY PUT CODE HERE >>>>DIRTY

I am guessing that somebody that didn't have any assembler knowledge found the text in memory, guessed the code was "NUDE", and sent the easter egg into a magazine to get their name listed. They probably guessed that nobody at the magazine would check the cheat worked, or that if they did have the game that they mustn't have typed it at the right time or the cheat only worked for the retail version. The easter egg was printed, and most likely other readers copied the easter egg and also sent it to all the other magazines to print. And before you know it, every magazine had printed this nonsense.

Most magazines incorrectly stated that typing NUDE on the title screen sends you straight to the boxing sub-game that occurs just after completing levels 2 and 4. But this is also nonsense.

The only reference to the memory address $1e23f is in the following code that is run whenever the main Dynamite Dux title screen appears:

_1cfaa  move.b  #4,(_0c6b3).l
        clr.b   (_0c6b4).l
        clr.b   (_0c6b5).l          ;Reset alternate intro flag
        cmpi.b  #'D',(_1e23f).l     ;Check for the 'D' in 'DIRTY'
        bne.w   _1cfe0              ;If not, skip ahead
        cmpi.l  #'IRTY',(_1e240).l  ;Check for the 'IRTY' in 'DIRTY'
        bne.w   _1cfe0              ;If not, skip ahead
        move.b  #1,(_0c6b5).l       ;Set alternate intro flag
_1cfe0                              ;Continue with intro sequence

Address $c6b5 stores the alternate intro flag byte, which is set to 0 to begin with. The game then checks if the 5 bytes at $1e23f are "DIRTY", and if so, sets the alternate intro flag byte to 1.

When the joystick fire button is pressed to begin the game, the code looks for the alternate intro flag byte and if it's set to 0, it loads $4800 bytes from offset $12e00 on the disk. If the flag is set to 1, the game loads alternate graphics from offset $e200 on disk.

Clean intro graphics

Dirty intro graphics

Cheat Mode

The game has a built in cheat mode that activates a level skip. On the title screen, simply type the letters from the word CHEAT to activate it. You can type any letters in between, as long as you type a C, then at some point an H, an E, an A and a T. The game stores the word CHEAT in rawkeys ($33, $25, $12, $20, $14) at address $1d525, and the game checks the code at $1d1a4.

As seen on Guru Larry

Guru Larry has created a video of my discovery, which you can view on YouTube.