This fascinating article [1] on the history of SMB hacking in Japan gives some more details on Minus World-like worlds and how they could be manipulated by "hot

This fascinating article [1] on the history of SMB hacking in Japan gives some more details on Minus World-like worlds and how they could be manipulated by "hot swapping" Famicom cartridges. "Players quickly figured out that it was possible to access levels beyond 8-4 by hot-swapping cartridges. What is positively known is that in 1986 a magazine called “FC Bug Boy Special: Super Mario 256W ” was released by JICC Publishing Office in Japan.3 This magazine detailed how to access worlds beyond 8-4 with the hot-swap method.4 It also included data tables and information about these mysterious levels.5 This publication most likely helped information about “256-World” spread through the budding player/hacking community." This ultimately led to the release of the Tonkachi Editor, sort of like a primitive Game Genie where you could laboriously modify memory to more precisely hack together your own levels. "It was a binary editor, but far from the sophisticated software available on today’s computers, it was light and simple at best, and could only patch data displayed in hexadecimal or ASCII code, not move or copy data. Since there was no environment, of course, no printout was possible. Moreover, due to the nature of quick disks, subsequent files could easily be destroyed if they were rewritten on a different drive or other device, and recovering them required a great deal of effort. In fact, even now that I am accustomed to using a Tonkachi, a task that can be done in a few minutes on a PC can take up to an hour or two on the NES if you use a Tonkachi." This ultimately resulted in a ROM Hack version of SMB called Tonkachi Mario released all the way back in 1987, at least a decade before I'd have assumed such hacks were being released. [1] https://glitchcat7.com/the-complete-history-of-kaizo-mario/ https://glitchcat7.com/the-complete-history-of-kaizo-mario/