GBA extra content hacked into SNES original.

Hi everyone. How hard would something like this be to pull off? Would the rom need to be expanded for the extra content to fit?

Some of the content would be easier to hack in than other content, but none of it could probably be called anything actually approaching easy.

With the spells and new weapons/armor/etc, the existing lists are already full. It's not just a matter of expanding the ROM; the lists are set up with IDs from 00h through FFh -- that is, 256 total IDs, for 255 items + 1 "empty", or 256 different spells/abilities. (Enemy spells, blitzes, bushido/swdtech, lores, etc. are all part of that same 256 'spell' IDs.) To include additional items, you're looking at two possible solutions. One, something like what they've done with FFVI Advance, where the new items share existing item IDs but their quantity value is 80h higher than the actual quantity (having 1 in inventory = quantity value of 81h; 99 in inventory = quantity of E3h (63h+80h), etc.); this would require some pretty extensive ASM hacking of the code which handles both inventory and equipment. Two, replacing existing items with the ones you want to import, which is simpler but means removing existing content from the game to make room. Spells are much more complicated: there's no second value that's easy to modify like quantity is for items, so again your simpler solution is to replace existing spells (although I do wonder if something could be done involving the Special Effect byte? something to look into, maybe, for general hacking use).

Adding the espers runs into similar issue: while I believe there's space on the esper bytes to allow up to four (possibly five? I don't recall if we need an "empty" bit or not) additional espers, you run into issues of space with a) the esper sprites (Leviathan and Cactuar can probably get away with existing sprites -- Cactuar as is, Leviathan as some variety of recolor from someone/something else) and b) again, the esper attacks are part of the spell list, and there's no space on that without removing something else to make space. So far we're looking at least at eight spells that would need to be removed to make space -- four for the new spells the espers teach, four for the esper attacks themselves. (... Possibly seven, actually; now that I think about it, I'm not sure Cactuar teaches any new spells, just old ones at better rates. Nonetheless.) The esper bonuses are a little easier -- I think there's only two new bonuses, one of which already exists in the code (speed + 2, iirc?) and one of which (HP+100%) is I believe listed in the coding but doesn't actually function.

As for the new dungeons: I can't really speak to these; I haven't done any map editing yet at all. From what I've read, though, the task would be herculean at best.

TL;DR: it's probably theoretically possible to include all the additional content, but I don't think anyone's going to be releasing a patch any time soon.

That might be an interesting site-wide project if we can get through the 15-th Man project... then again, its 99% ASM work since there's not a lot else to be done, but maybe a colaboration project with the coders on the site... I should really try to focus on one thing at a time.