I was just wondering: it is possible to add a ninth world to NSMB?

Cause frankly I had a killer idea for my hack in my dreams which consists on dark corrupted "World 9", which would work as like a very secret extra world in the game

^{another question is if anyone has actually done it before}

Nobody has never ever done it, and making that would probably take decades
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Damn.

Well maybe I can be the first one to do it





^{although ASM hacking is not my strength}

Well, that would require extensive ASM knowledge, and there's a reason no one has done it yet
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You'd have to make new world map data (and model) and assign world IDs as well but as said here that's hell, as even making a world map model isn't as easy as it looks like

Heap space is a matter as well, so even if one succeeds to add new worlds there will be less heap space left to add other ASMs (unless overlays are used)
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its been done before, just its really hard. iirc, it was unused in newer

newer didnt attempt it, but it isnt that hard to do and people have made attempts. Most of them lost motivation before they could finish though