jetsetdanny

Ah, that item you're referring to is in an 'odd' column number, so nothing is printed there for a Willy sprite in its leftmost frame of animation. (Well, technically the value #00 is written there, but that's what was already there anyway as it's an air cell in a room with a black background, so nothing changes in that cell and the item remains collectable. Try setting the dancing lives to a different animation frame and I think you'll find that it's uncollectable.)
Conversely, the auto-collected item in Kong Beast is in an 'even' column, and it's actually one of the spare Willy's front foot which 'collects' it - the byte value for his feet in that position is #77, the first 7 represents his back foot, the second digit is his front foot, and that 7 is interpreted as white INK in the attribute buffer!

When Willy falls off the bottom of a cavern (or jumps up past the top), the corruption happens to the data of certain caverns, so you would have to reload the game file to reset it. (Same with the Attic Bug in JSW.)
The spare lives overspill is happening in the buffers, so it's not permanent. If you lose some lives, then it will start to become undone (the errant blocks will retreat from right to left across the screen.)

So you could envisage a scenario where progress relies on turning the music back on to make a block change from a lethal Fire cell to a 'standonable' floor block! The on/off status of the in-game music being an inherent part of the gameplay would be another novelty!

Not shown in the video because I just wanted to get something out there quickly, but what's actually drawn on the screen depends on the sprite shown for Willy's lives; as I have the music turned off, it's not cycling. The state I have the sprites paused in is the only state in which items are auto-collected. In all cases at least one of the two blocks drawn is a floor block. I suspect the black cells are actually air tiles, hence the item being collectable; these same black tiles are nasties in Skylab Landing Bay.
 
I actually discovered this a while ago with lives POKEs, this was just my first time seeing if it can occur during normal gameplay. You can experiment yourself with POKE 33879,n. After 48 lives, they start being drawn over the level name and air counter instead.
There's a limit to how many lives you can have before each level becomes incompletable (although you can always lose lives until they become completable again). I've split them into three groups:
 
Early blockers:
Central Cavern - at 39 lives, you cannot jump over the robot without landing on the extended platform, which blocks your fall to below. Interestingly, it becomes possible again at exactly 46 lives only, as this allows you to walk to the right and drop down that way (similar to what the GBA/PC version allows you to do), but at 47 lives that way becomes impassable too.
Miner Willy meets the Kong Beast - at 40 lives, there is no way of getting through the opening after pressing the switch to collect the last banana.
Endorian Forest - at 40 lives, the middle trunk and extended platform seal you in the starting section.
Return of the Alien Kong Beast - 40 lives, same as Miner Willy meets the Kong Beast.
Skylab Landing Bay - at 34 lives, the nasties block a mandatory path.
The Final Barrier - at 46 lives, there is no way of getting out of the top-right area after collecting the keys there.
 
Standard blockers:
At 47 lives, the "platform" extends covering the entire play area (minus the last two cells, but one of those is always a wall, and Willy can't fit through a gap of one cell). For The Cold Room, The Menagerie, Eugene's Lair, Processing Plant, and The Warehouse, 47 lives is the point at which they can no longer be completed as the entire screen is blocked and cannot be traversed from top to bottom.
 
No blockers:
These come in two forms: in Abandoned Uranium Workings, Wacky Amoebatrons, The Bank, The Sixteenth Cavern, Amoebatron's Revenge, and Solar Power Generator, you start in the bottom half of the screen and exit at the top. As a result, platforms stretching across the screen don't inhibit progress at all. You do normally need to revisit the bottom half of the screen in Solar Power Generator, but the platform extends to make that unnecessary long before it's made impossible.
The second form is in The Vat, Attack of the Mutant Telephones, and Ore Refinery. While all three of these levels require going from top to bottom to top (or bottom to top to bottom in the case of Ore Refinery), they also have platforms very near to the top of the screen, requiring wall tiles to prevent you from jumping outside of the screen boundaries. These wall tiles are replaced with floor tiles, allowing you to jump through the screen vertically and access the other half of the screen.
All of these levels can be completed regardless of the number of lives you have.
 
Whether it should be allowed or not is already contentious enough with what I've already shown - I think we can safely say that if cheats are required then it definitely shouldn't count, so anything with extensive corruption is out. I believe this also means that the maximum attainable life count in the game is 38 (Skylabs limiting to 34 plus four extra lives attainable in one loop).

True! It occurred to me just after I posed the question that, whilst perhaps slightly novel, it wouldn't present any additional difficulty to the cavern, because the player would (for a 'standard' Kong-style cavern) have to pass through there anyway.
However, musing on it a bit further, I think I have thought of a possible cunning use for it... I feel another quirky one-cavern puzzle might be in the works...

I don't recall anything like this.
However, functionally this wouldn't be different from what usually happens - if the wall that collapses after the first switch is tripped blocks access to a part of the room where some items are, these items are only collectable after the first switch has been tripped (because prior to that they are unreachable).

That comment has just inspired me to wonder - has there ever been a MM game with a Kong cavern where an item is embedded within the collapsing wall, and therefore only collectable after the first switch has been tripped? 🤔

It seems that it's still collectable when another attribute is printed over an item - this happens in Abandoned Uranium Workings. It also seems that the bug is consistent in what it puts on-screen. My main concern is that it isn't possible the first eight (at minimum) times you complete the cavern, and these are clearly different caverns to those intended due to modified terrain.

Duck - that is very much in keeping with the level of obsession about all things JSW & MM
related on these forums, excellent work! You also have more free time than I do! But top effort!

Okay, I've just seen the caveat at the start of your video. (EDIT: This post crossed over with DD's latest reply.) On that basis, whilst it's a very interesting and quirky experiment, I don't think it should form the basis of an update to the ranking table?
As you suggest, it isn't something that can be achieved in the High Score Challenge, because it relies on the player having completed all 20 caverns several times through beforehand! Which isn't something you can do in the HSC; you just pick a cavern and play it (slowing your score for that cavern easily to be seen, since you start off with 000000)
Also, the high scores in the table at the start of this thread should serve as a target for the average (good) player to aspire to. I don't think activating this bug is within the bounds of normal/sane gameplay!
Plus the precise outworkings of the bug may be somewhat predictable. In one cavern during your experiment, an errant extra life auto-collected an item (presumably because the INK in the host character space was rendered in white). But in other circumstances, a non-white INK attribute might get printed over an item, making it uncollectable!?
Those are just my personal musings; ultimately it's Andy (Spider)'s call as to whether to update the high score table, since it's his project.

I played through, albeit not in real-time (so savestates, rollback etc.) - I'm doing it for a max score run because I think it's interesting to watch the game disintegrate as you play.
It takes about two hours of perfect play to get to this point so I don't recommend it.

In short: earning enough extra lives corrupts the screen, which acts as floor tiles in most caverns and allow routes that aren't normally available.
The following five scores are shown in the video:
Abandoned Uranium Workings - 1856
Miner Willy meets the Kong Beast - 4142
Wacky Amoebatrons - 1377
Attack of the Mutant Telephones - 1750
Ore Refinery - 1884

Will hold off updating a couple of days (unless you want to update the file descriptor @IRF ? ) until @DigitalDuck finishes the experiment. 🙂

If the above statement is correct (quoted from the first post of this thread), then I can't think how you managed to achieve a higher score in that (or any other) cavern of the BB* version than you can in the High Score Challenge version!?
(*The HSC is based on BB, so it is possible to achieve one extra point in the SP version's 'The Warehouse', because the different sprites there means that Willy can sneak past the last one, one time-frame sooner. But that doesn't apply to 'Abandoned Uranium Workings'.)

It doesn't use any POKEs, it's possible in both the original Bug-Byte and Software Projects versions without any modifications.
However, it's not possible in the high score challenge version of the game.

Intriguing... I would say that if it involved the use of some quirky feature of the existing game engine, then it should count. But if you used a POKE of some sort, then it shouldn't.

I've managed to complete Abandoned Uranium Workings with 1856 points, but it's in a very non-standard way and probably shouldn't count in the rankings... I'll reveal more when I'm done exploring other levels.

Maybe he's a fisherman, and in the spirit of Matthew's double entendres, it's called 'Willy's Big Tackle'. 😜

Dynamite Dan II
Dynamite Jet Set 😉 Ideally with an ending this time 😮

Sounds like a great idea for another game...

But then if Willy's first adventure was set on a chain of islands, it wouldn't have been called 'Manic Miner'! It would have been 'Willy the Island Hopper' or something, and he would be wearing a sunhat or visor instead of a miner's helmet.

I'll check and if necessary update the rankings in the download over the weekend.
Thank you! 🙂

This is one of the main reasons I *always* play using Rollback. It allows me to progress efficiently through games while solving them "relatively honestly", i.e. without using an Infinite Lives- or any other POKEs. If I were to try completing a game with only seven lives (or even 20, or 50), I probably wouldn't be able to do it at all, and if I really had to do it, I would have to spend weeks and possibly months training to achieve it. I would consider that an utter waste of time - and that's referring to my otherwise beloved JSW and MM games.

Hear! Hear!

Yes, I've experienced it too. It is an additional difficulty, and it is frustrating 😵.