This was an attempt to backport a hidden mode originally found on the Game & Watch Super Mario Bros. from 2020.
It's not perfectly the same behavior as the original, but there were just enough unused functions, data, and code to remove and then squeeze in this functionality without requiring a mapper. Unfortunately, efforts to additionally fit the option to choose a difficulty were unsuccessful.
This project has concluded, so anyone is welcomed to improve upon it independently.
The patch has been fully tested on original hardware and has been completed successfully without issues.
Hint: you need to do something on the title screen to activate this mode.
Size: 40976 bytes (40 KiB)