Ms. Pac-Man (Arcade)
Originally developed by General Computer Corporation as an enhancement kit for Pac-Man called Crazy Otto, Ms. Pac-Man's huge success eventually made it an official part of the franchise (most notably the 1982-83 Pac-Man cartoon). 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 Ms. Pac-Man that they produced unauthorized ports without returning royalties to GCC, leading to a years-long legal battle over the IP rights.
The game itself 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, which went to a fifth (purple) ghost for the aforementioned cartoon and subsequent games.
In the game's graphics data, there are 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 games. However, they were eventually incorporated into Jr. Pac-Man (when a bonus item runs over a regular dot).
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.
A leftover key graphic from Pac-Man, a "fruit" that is not present in 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 x 4, Left x 4, Right x 4, Down x 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) to ($8D2):
Super Pac-Man was an in-development title for Ms. Pac-Man, as explained by programmer Steve Golson during GDC 2016. This title predated Ms. Pac-Man but succeeded Crazy Otto. One year later, Namco would create and release their own Pac-Man sequel with this title (see: Super Pac-Man) (In the game's text map, the @ symbol is used for spaces, and semicolons are used for hyphens.)
Located at ($D5A) to ($D60):
The name of the red monster in Crazy Otto.
Located at ($D79) to ($D7E):
The name of the pink monster in Crazy Otto.
Located at ($E51) to ($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 to 0x97FF), a small message from programmer Steve Golson can be read:
GENERAL COMPUTER CORPORATION Hello, Nakamura!
Masaya Nakamura is 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.