Standard & Poked version (Phantomz) : 

 " Bubble Bobble ", the original version by Firebird released in 1987.
I know we have the new fantastic Bubble Bobble remake (BB4CPC) by Csar Nicolas Gonzales available to play now, however I also wanted to play the version that I used to play as a kid.   ;)
The game is now Joypad/s only, Button 1 to Shoot, Button 2 to Jump.
Pause / Unpause with console pause button, can't pause the game in the final encounter ( Part 2 ).
Joypad 1 Button 1 to Start a one player game, Joypad 2 Button 1 to Start a two player game.
If you play a two player game, you receive eight credits, Use Joypad 1 Button 1 to continue for player one and Joypad 2 Button 1 to continue for player 2.
In Bubble 1 ( part 1 ).
I've removed the need of the access code completely, when you complete part 1, you will now see " NOW PLAY THE  FINAL ENCOUNTER " instead of " ACCESS CODE FOR THE FINAL ENCOUNTER, ZZZ13VWZZZZZZZZZZZZZ1WVZZ1Y24V2W ".
In Bubble 2 ( part 2 ).
When you load part 2, you will see " LOADING " instead of " TYPE IN CODE ", you would normally have to type in the access code here, or even type in anything to load the game, however instead of trying to change the code or even having to keep pressing any keys, I've made it so that you don't need to type or press anything to load the game.  8)
I've included a poked version which gives infinite lives for both players in both parts.


Select nb of button (pmeier) : 

The version by @Phantomz is perfect, I just wanted to add a nice menu to enable one or two button(s) joysticks. I have no GX4000, so I also added the disk, which contains my assembler sources.
Credits go to
@Phantomz for his ROM. I simply diffed snapshots, so that I don't have to find out memory locations. (Is there a better way? Are the changes somewhere documented? Is it possible to extract files from the ROM??)
ACS: For his loader. It loads the unmodified OEM files. (I have also the original boxed disk version.  8) )
For the boss fight I also changed key 1/2 to player1-fire1/player2-fire1 to continue, although you have enough lives to beat him.
I haven't updated the messages like @Phantomz ("R to redefine keys" makes no sense in my version), because I wanted everything as close as possible to the original, but I see that you wanted to be perfect.