Under the microscope: Planet Joker (Saturn)
I'm the Joker, baby!
In this edition, I’m examining Planet Joker, the 1997 shooting game for Saturn. This game doesn’t have a whole lot of fans because (a) it was never released outside of Japan, and (b) it’s kind of clunky and weird.
I found some cheat codes that will make sampling this game a bit easier, however: one grants you unlimited health; another allows you to start on any stage and upgrade your weapons.
Details about the codes and how they work are below!
Unlimited health
At the mode select screen, hold Z+Left and then press Start when choosing a mode.
This will grant you unlimited health – you’ll never run out of shield capacity. For reasons I don’t understand, the shield gauge in the bottom left will go down if you take damage, but it won’t ever go to zero:
Mission select
Start a game in normal mode. At the Machine Select screen, hold Z+Up, then press A to choose your mech. Keep holding all three buttons.
If you got it right, the barebones stage select screen will appear:
StageNO allows you to pick your starting stage, of course. Values 1 through 6 are the normal mode missions. Value 7 is the time attack mission:
Value 8 is the score attack mission:
Value 9 is the boss attack mission:
The menu allows you to choose higher values, but the game will crash if you do.
ShootKind and ShootLebel (sic) affect your primary weapon. The only valid values for the former seem to be 0 and 1. The latter has a higher range, but I couldn’t quite figure out all of the distinct effects:
Technical details
I found these cheats by using my usual method:
Locating where the game stores input by comparing memory snapshots taken (a) while holding a button, and (b) while not holding a button.
Setting read breakpoints for the memory addresses associated with input.
For this game, the “held button” is stored at 0602b4b8. The function at 06004390 checks it when you make a selection at the mode select screen. The logic looks like this pseudo-Python:
if held_button & (Z_BUTTON | LEFT_BUTTON) == (Z_BUTTON | LEFT_BUTTON):
play_sfx(0x105)
WORD_0602b318 = b'\x00\x01'The 2 byte value at 0602b318 determines whether the game continually resets your health to a value of 12 during gameplay.
The function at 06006690 does a similar check after the machine select screen. It looks for Z+Up+A being held. If it is, it sets the “game mode” (at 0602ce60) to 9, which is for the debug screen.
I looked for a way to unlock the extra mech with a cheat code, but didn’t find one. You should be able to do it with this Action Replay code, however:
1602b354 0003
The character select handling function (at 060ad404) checks the value at 0602b354 to see whether it’s greater than 2. If it is, it sets the mech limit to 7; otherwise it keeps it at 6.
Outro
For many more adventures in retro game reverse engineering, see my archive here at Substack.
There will be more articles this week. If you’ve got suggestions for games that might be harboring secrets, leave them in the comments.
