Ms. Pac-Man (Arcade)
Originally developed by General Computer Corporation as an enhancement kit for Pac-Man called "Crazy Otto", Ms. Pac-Man is an improvement over Pac-Man with changing maze layouts, new cutscenes, new sounds and music, and the bonus items bouncing around the maze. The orange ghost was also renamed from Clyde to Sue, giving some female representation among the bad guys (the Pac-Man cartoon, which debuted later in '82, had both ghosts; Sue was instead purple, a distinction that would carry over into subsequent games).
Contrary to popular belief, Namco cleared Ms. Pac-Man for release and contributed to the character's design. In fact, Namco was so eager to profit from the game that they later produced an anniversary-themed cabinet without adhering to a royalties contract they agreed upon with GCC after the game’s cabinets initially ceased production, leading to a years-long legal battle over the IP rights.
The game's graphics data includes three types of dots: the regular ones, the Power Pellets, and an unused medium-sized type in between. The medium dots appear in the code of Pac-Man, Pac-Man Plus, and Ms. Pac-Man, but go unused in all three. A variant was eventually used in Jr. Pac-Man for when a bonus item runs over a regular dot, with them slowing Jr. down a bit when eaten but rewarding the player with a couple more points than usual.
The logo for General Computer Corporation is present among the graphics, probably a leftover from the game's days as "Crazy Otto".
An unknown graphic that seems to be partially cut off.
The graphic for Keys, a "fruit" that is present in Pac-Man but not Ms. Pac-Man.
As Ms. Pac-Man runs on top of the Pac-Man ROM, the Easter egg from the original game is still present and functions in the same way: enter Service Mode, then quickly toggle it off and on. A video alignment grid will appear on the screen. Hold P1 START and P2 START and toggle Service Mode off and on again. If you've done it right, the grid will stay on-screen. Now, using the joystick, press Up (×4), Left (×4), Right (×4), Down (×4).
If you've done it right, "MADE BY NAMCO" will appear on the screen in red Power Pellets.
Original Ms. Pac-Man hardware consisted of a daughtercard containing encrypted ROMs that plugged into the Z80 socket on a standard Midway Pac-Man logic board. Those encrypted ROMs would decrypt and apply a patch in real time to the original Pac-Man ROMs (still present on the logic board), but decrypted romsets (commonly used on bootleg hardware) are pre-patched, essentially doing away with the daughtercard and the "real time patch" method. Poking around in the decrypted/patched 6J ROM (pacman.6J in the encrypted "mspacman" romset, BOOT4 in the decrypted "mspacmab" romset) yields a couple traces of Ms. Pac-Man's development.
Located at $8C6-$8D2:
(In the game's text map, the @ symbol is used for spaces, and semicolons are used for hyphens.)
"Super Pac-Man" was an in-development title for Ms. Pac-Man, as explained by programmer Steve Golson during GDC 2016. This title predated Ms. Pac-Man but succeeded "Crazy Otto". One year later, Namco would create and release their own Pac-Man sequel with this title.
Located at $D5A-$D60:
The name of the red monster in Crazy Otto.
Located at $D79-$D7E:
The name of the pink monster in Crazy Otto.
Located at $E51-$E56:
Text used for the service mode of Crazy Otto, where the operator can set the number of lives the player is given (listed as "PAC-MEN" in Pac-Man and "MS PAC-MEN" in Ms. Pac-Man).
Loaded at the end of ROM memory (0x97D0-0x97FF) is a small message from programmer Steve Golson:
GENERAL COMPUTER CORPORATION Hello, Nakamura!
"Nakamura" refers to Masaya Nakamura, the founder of Namco. Jr. Pac-Man also has this message, as GCC also developed that and reused Ms. Pac-Man's assets.
This message is still present in Ms. Pac-Man & Galaga: 20 Year Reunion, which led to a lawsuit as GCC successfully argued that they were not being paid royalties for the use of their work. Some ports following the litigation, including the Ms. Pac-Man Arcade1UP releases, seemingly blanked out the message entirely.