Although 'Mary Shelley's Frankenstein' is a 4-player game, it played a role in the development of the 6-player feature used on subsequent Sega games. Programmer Orin Day tells us about the use of 6-players in Sega games:

The 6-player display code was prototyped as a "proof-in-concept" on the Frankenstein display, but was first released in Baywatch. The Frankenstein multiball start display effect was repurposed in attract mode to promote this 6-player feature. Baywatch and Batman Forever also had this feature. When we switched back to the 128x32 display for Apollo 13 and subsequent games we also switched to the Whitestar hardware system. It's my recollection that at that time we coded both the game and display to take six players. It was removed from the system at the time of Sharkey's Shootout, no games after that had it (with the exception of NFL, which was a derivative of Striker, and any games from earlier in the catalog like South Park which were remanufactured).