That's a cool mod. I also started doing mods to re-balance a game. Jungle Lord in my case. I could not think of a switch mod like yours to solve the main problem I had with the game so I went the software route. I have come to really enjoy modding WMS pinball software, which is what started the conversation with @ss-pinball. Overall, I enjoy FP2 on my tablet, but I do not like the ramp shot very much. I have never played an FP2 "in the flesh", so I don't know if I like it enough to want to buy it and spend 100 hours plus to disassemble and analyze the software.

The problem with modding system 7 game software is that there is very little space in the ROM to begin with. (Jungle Lord literally had zero bytes free and I managed to free fewer than 100 bytes for all my mods.) So what's achievable depends very much on what is already in the ROM somehow. For example I managed to implement a ball saver in Jungle Lord with only a few bytes because there is already something like a ball saver that's part of the original game rules. Implementing a multiball jackpot, like you suggest, is likely beyond what there is space for. Problem is you cannot tell for sure before you have essentially analyzed the entire game ROM.

That's right. Empty blocks are filled with hex FF. I just checked the ROMS from IPDB: there are not two consecutive bytes filled with FF in the entire game ROM. That's the same in Jungle Lord. I am guessing that the programmers implemented the games and then filled the remainder of the ROM with light and sound effects. I can make some space by removing audit updates and optimizing a few bytes of code here or there, but that likely won't give me more than a few dozen bytes at most and there's not much in terms of rule changes that can be done with that.

For the Jungle Lord home ROM I used information from Jess Askey's web archive at http://gamearchive.askey.org/Pinball/Manufacturers/Williams/PinBuilder/text/williams_lvl7_programming.html. More recently I have written my own disassembler and compiler for System 7 - 11 code. One of the main benefits is that the compiler can optimize source code to make some free space available.

@quench, I have not done this with Jungle Lord because I wanted to make a Home ROM that is easy for others to install, and because I found other ways to free sufficient space for what I wanted to do with the game. But you are correct, of course, expanding the system-7 ROM space is easy enough. What's really stopping me from getting my teeth into the FPII code is that I do not have access to a copy of this game and I do not like working with emulators.

To make this useful I will first have to write documentation. Williams System 7 to 11 games are programmed in a mixture of M6800 assembly and a byte code interpreted by a virtual machine. For my tools (7eleven) I invented a human-readable language for the disassembled code mixture. There is no documentation for my version of this language.

However, there are tools and documentation available for system 7 games. For Jungle Lord (new tricks) I used Jess Askey's PinBuilder (http://gamearchive.askey.org/Pinball/Manufacturers/Williams/PinBuilder/). Jess' tools include a disassembler with example configurations for several system 7 games. Not all of the documentation is completely clear. I am happy to provide clarification and additional explanations.

You should ground your game. It's a safety thing.