Dr. Mario (Game Boy)
This game has a notes page
This game has a bugs page
Dr. Mario is Nintendo's own little action puzzle game, where Mario throws pills into a jar to get rid of viruses.
Present within the ROM is a second gameplay demo meant for when the player idles at the title screen, though the demo recorder in this case does much worse than the standard one.
FFA9 "program number" 00/01 - player select 02 - demo 1 03 - demo 2 (unused) 04 - pill falling 05 - game end 06 - 2 player outcome screen (draw/win/lose) 07 - cutscene 1 08/09 - unknown 0A - pill dispensing 0F - miss 10 - clear
There is code that was supposed to fill the top part of the game board. It was "fixed" with a jr instruction.
Unused Level Configurations
For the virus placement algorithm, there are two tables filled with values that, when added together, do not surpass 0x66.
The index to these tables is the level selected. The base addresses are:
t1 = 0:311B t2 = 0:313A
And the code that reads from these tables is at 0:3076.
These tables are side-by-side in the ROM, and each table is 31 (0x1F) entries, though only in Rev 1 (see below as to why). In code (located at 0:101C), the max level limit is 30 (0x1E).
Because there are only 20 selectable levels, it's a good guess that the developers probably didn't intend players to get too far past Level 20 (not helped by a bug related to the viruses that can softlock the game; see the Bugs page for more).
You can access this entry by changing the level selected byte (0xFFC3).
Rev 1 added six more levels, with the game looping Level 30 repeatedly. The original release had 24 levels (and looped Level 24 repeatedly), with an unused 25th.
Rev 1 also removed a duplicate "2 player GAME" and "(c) Nintendo 1990" tile map.
The other changes made with Rev 1 consist of minor offset calculations and header updates.