IRF

For this reason, I will probably record v. 3 in the same way I have recorded versions 1.05 and 2 - in three different speed modes. In case of v. 3, each speed mode will also present a different order of MM caverns (the third one being the random one).
I am currently working on v. 2 video, if all goes well I will upload it to the JSW Central later tonight (I've got a few hours left since I'm in the western hemisphere right now 😉 ).

So the only difference between modes 3 and 4 is 'behind the scenes' - the order of caverns to be encountered is determined (shuffled) at the start of the game, or else they are randomly selected as the game proceeds. But from the player's perspective, they are identical. (Although I suppose in the former case, the random order must be listed at some memory addresses, so a hacker could PEEK in advance (if they knew the right address) and find out which cavern will come up next? 

Penelope58, thank you for your post, but... are you a person?... or a bot??? 
I'm asking this because while I whole-heartedly agree with the comment you posted, its content is just an edit of my initial comment in this thread, slightly modified, as ChatGPT could have done.
So I wouldn't be surprised if you posted several such messages, to "authenticate" yourself, and then started to spam us with non-JSW related things...

Hi Guys,
As someone familiar with the game, I highly encourage everyone to give it a try—not just a quick look, but play it through to the end! It’s possible to complete without losing a single life (though it’s quite a challenge unless you save/reload snapshots or use Rollback! 😉). This masterpiece combines Sendy’s brilliant design with Erix1’s enhancements to the JSW48 game engine, offering visually stunning elements and engaging gameplay challenges.
The game also has an interesting history. A beta version was shared in the now-defunct MM/JSW Yahoo! Group back in 2004, but the much-anticipated gamma release didn’t happen at the time. For those who remember those days, the long wait has been worth it—what a fantastic comeback by Sendy!
Don’t miss out, play it to completion, and keep an eye out for Sendy’s other promising projects. 🙂

By the way, in your test_fall demo, it looks like Maria has catched up Willy with the last unopened bottle.... what Willy was just going to "tidy up".😆

Thank you for your demos, Spider! They made this very clear! ☺️Thank you, too, IRF, for the fun fact! 🙂I think there should be lots of toilets positioned in every room in every JSW game to save Willy falling too far!😋

And a quick demo, no player interaction needed other than to start the game:
test_fall.tap
 
Same 'base' as the other two test files, ie: OK for editing for testing not really recommended for building a whole game from.
EDIT... Updated very slightly, now Willy has the choice of moving left to collect the single (wine bottle) item from Top Landing or go to rightwards to explore.
A little care should be taken with when he grabs the item with regard to the descending razor blade guardian! However if he does lose a life, upon re-materialisation he'll clear it on his automated run.

Fun(?) fact: if you extend the Bathroom ramp all the way down to the floor, and put a hole in the upper platform directly above the toilet, then during the toilet run Willy will run up the ramp and drop through the hole... But will disappear halfway through the fall... then appear suddenly in the toilet. (ie Without visibly falling through half of the height of the room.)
This is because the code which tests for Willy's coordinates at the end of the toilet run doesn't check which vertical half of the room he is in.

(But of course, when he is eventually drawn with his head down the toilet, he is in the correct location - bottom-right corner, bottom half of the Bathroom.)

Fun(?) fact: if you extend the Bathroom ramp all the way down to the floor, and put a hole in the upper platform directly above the toilet, then during the toilet run Willy will run up the ramp and drop through the hole... But will disappear halfway through the fall... then appear suddenly in the toilet. (ie Without visibly falling through half of the height of the room.)
This is because the code which tests for Willy's coordinates at the end of the toilet run doesn't check which vertical half of the room he is in.

Fun(?) fact: if you extend the Bathroom ramp all the way down to the floor, and put a hole in the upper platform directly above the toilet, then during the toilet run Willy will run up the ramp and drop through the hole... But will disappear halfway through the fall... then appear suddenly in the toilet. (ie Without visibly falling through half of the height of the room.)
This is because the code which tests for Willy's coordinates at the end of the toilet run doesn't check which vertical half of the room he is in.

(But of course, when he is eventually drawn with his head down the toilet, he is in the correct location - bottom-right corner, bottom half of the Bathroom.)

Fun(?) fact: if you extend the Bathroom ramp all the way down to the floor, and put a hole in the upper platform directly above the toilet, then during the toilet run Willy will run up the ramp and drop through the hole... But will disappear halfway through the fall... then appear suddenly in the toilet. (ie Without visibly falling through half of the height of the room.)
This is because the code which tests for Willy's coordinates at the end of the toilet run doesn't check which vertical half of the room he is in.

It does. A number of games are only toilet-completable thanks to this feature.

Doesn't pressing P during the toilet run stop him in his tracks? 

Doesn't pressing P during the toilet run stop him in his tracks? 

The ability to slow the game down would be useful for the room 'The Garden' in JSW2 [original version], the crossing of which requires a succession of well-timed, pixel-perfect jumps.  :o

I just had a thought - is it theoretically possible to complete the original Jet Set Willy without applying any POKES, not even the four officially released ones?
The Attic Bug corrupts the game data and code in unpredictable ways, so unpredictable that the effects are different every time you play the game. Might it be possible in theory that one effect could be to corrupt the list of guardians in both Conservatory Roof and First Landing, creating an arrow which passes along the character row where the items are located in each of those rooms (an invisible item, in the latter case).
Were that to happen, then the white INK of the arrow would auto-collect the items that otherwise can't be collected without using the official POKES, and so the unPOKED game could in theory be completed (provided Willy can manage to complete his journey through the corrupted mansion without one of the many other side-effects of the Attic Bug getting him!)

The walkthoughts were possibly (likely?) mine, I've done several.
Certain rooms however when the bug is in effect do seem to make it deteriorate a bit faster, notably "Inside the MegaTrunk" , staying here and switching emulation speed up a bit (200% is fine) you'll see the status bar start to corrupt. Kitchens can have a similar effect, although the guardians moving horizontally at that stage is erm distracting.
 
A sidenote about the other "big three" bugs: I think half or most of the battle is Banyan Tree, if it were possible to jump from the left side and catch onto a water cell without hitting a guardian, you could then climb it. The "First Landing" object something would have to be done or the item count adjusted to ignore it, same perhaps as "Conservatory Roof"

I just had a thought - is it theoretically possible to complete the original Jet Set Willy without applying any POKES, not even the four officially released ones?
The Attic Bug corrupts the game data and code in unpredictable ways, so unpredictable that the effects are different every time you play the game. Might it be possible in theory that one effect could be to corrupt the list of guardians in both Conservatory Roof and First Landing, creating an arrow which passes along the character row where the items are located in each of those rooms (an invisible item, in the latter case).
Were that to happen, then the white INK of the arrow would auto-collect the items that otherwise can't be collected without using the official POKES, and so the unPOKED game could in theory be completed (provided Willy can manage to complete his journey through the corrupted mansion without one of the many other side-effects of the Attic Bug getting him!)

The corrupted guardians can cause corruptions themselves, but in an unpoked game Willy would just instantly die on entering those rooms preventing the enemies from corrupting the game further. The cheat POKEs in the video I saw were to prevent deaths from guardians, allowing them to cause further corruption.

Could it be possible that those cheat Pokes have corrupted the corrupted parts even more?

The effects aren't unpredictable and aren't different every time you play - the arrow's trajectory is consistent and writes to the same bytes every time.
To be precise, it corrupts the flying bird, UFO, Esmerelda, giant head, skull, sunflower, and Andre enemies, and any room those enemies can be found in result in the guardians being misplaced and (depending on the room) embedded into walls (which automatically kills Willy on room entry). None of those enemies can be found in First Landing, The Banyan Tree, or Conservatory Roof, the rooms that would need changes in order to make completion possible.
It's possible to complete Jet Set Willy without fixing the Attic bug, though - you can apply the other three POKEs (42183,11; 56876,4; and 60231,0), play the game as normal making sure to only climb the East Wall and get the items in Priests' Hole and Dr Jones and head into the Attic once you have all of the other items. From the Attic, you can go Under the Roof -> Conservatory Roof -> Orangery -> Swimming Pool -> Banyan Tree (left to right - not easy!) -> The Nightmare Room -> First Landing -> Top Landing -> Master Bedroom and complete the game.
You can't complete it twice though, because the rooms with those enemies in don't become accessible again even after beating the game.

The internal contradiction in the statement did occur to me (JSW vs MM), but then I suppose the in-game tune in Manic Miner doesn't play during the portal air countdown*, so in that sense it doesn't play continuously.
(*Except in Manic Mixup. 😉) 

I just saw this on a Facebook post:
"MATTHEW SMITH!
The creator of Manic Miner and Jet Set Willy.
Seen back when he was writing games, and then around 2013.
Jet Set Willy was the first game to include continuous music (such as music was on the Spectrum) while you played the game, a feat which up to that point was thought to be impossible.
He actually wrote Manic Miner on a Tandy TRS-80."
It got me wondering - is that claim in bold actually true?