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Youtube video here: https://youtu.be/E6qRbk5Cscw?t=1127

Most of the glitched worlds are clearly ROM fragments of world data being loaded, most of them out-of-alignment and being rather messed-up.

This one is somehow different. It's mostly but not 100% consistent; suggesting that its possibly loading some stuff from RAM instead of ROM. The characteristic of all the repeating clouds seems unique to it; and normal ROM data wouldn't look like that.

So what's actually going on here? What nonsense did it load? Is it in the middle of sprite data or something like that?

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    I vaguely recall some resource explaining the particular format of Super Mario Bros. maps in detail, which also explained how it managed to be so compact that basically any sequence of bytes renders into a more-or-less playable map. I do not remember where it was, though. Perhaps searching through sources under <retrocomputing.stackexchange.com/q/1672/15334> will be fruitful.
    – user3840170
    Sep 11, 2022 at 12:16
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    A nice high-level description of the various compression steps used to get all of Super Mario Brothers into 32K is given in this talk (youtu.be/TPbroUDHG0s), roughly between 5:45 and 13:00.
    – Michael Graf
    Sep 11, 2022 at 19:00
  • @MichaelGraf ?t=5m45s
    – user3840170
    Sep 13, 2022 at 13:06
  • I'd have to do some research but this video may help. At the timestamp 5:56 there's a table called "Tile Data Pointers" youtube.com/watch?v=B8o_VpY9scs I'm guessing that with the letter "T"'s ASCII code as your index (again, depends on the layout of SMB1's character rom) the table is indexed out of bounds and whatever it at that address is read and interpreted as a pointer to level data. Now that being said, it depends on what the resulting address of the "T" offset gives you, and how the tables marked "LO" and "HI" are aligned (if they even are.)
    – puppydrum64
    Dec 16, 2022 at 14:37
  • @puppydrum64: Turns out it's not so easy. The level map for T-1 returns a pipe transition that transitions somewhere else. I looked through all of the level maps on that guy's resource and none of them correspond to the video.
    – Joshua
    Dec 16, 2022 at 16:06

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