DigitalDuck

I like what you're doing with the levels graphically - it's definitely a lot more effort than I put into it when porting them to Redux (a PC remake; in general I didn't create or use graphics that weren't in the Spectrum games). I notice you've also made the same change to Cheese-Plant that I did (moving the key out of the corner so it can be collected).
We did have a big discussion over how to handle The Pink People Eaters with the original physics, as the way it is in the SAM Coupe relies on being able to stand half on solid ground and half on a nasty without death, which isn't possible in the original game. I have it implemented like this now:

Naturally other parts of this will be different in your implementation, but it's something to consider.
It looks great so far and I'd definitely be interested in stealing borrowing your sprite work when I work on this side of things again.

I like what you're doing with the levels graphically - it's definitely a lot more effort than I put into it when porting them to Redux (a PC remake; in general I didn't create or use graphics that weren't in the Spectrum games). I notice you've also made the same change to Cheese-Plant that I did (moving the key out of the corner so it can be collected).
We did have a big discussion over how to handle The Pink People Eaters with the original physics, as the way it is in the SAM Coupe relies on being able to stand half on solid ground and half on a nasty without death, which isn't possible in the original game. I have it implemented like this now:

Naturally other parts of this will be different in your implementation, but it's something to consider.
It looks great so far and I'd definitely be interested in stealing borrowing your sprite work when I work on this side of things again.

Making something run more efficiently doesn't have to mean speeding it up - it can be used to make the game run at a smooth speed (syncing to display refresh and counting frames) instead of speeding up when there are less enemies and slowing down when there are more, or add other more complex elements to the game.
Personally I think somewhere between original Manic Miner's Central Cavern with music off (about 12fps) and the GBA version (20fps) is a good speed, which is why I set the default speed to 15fps in Redux.

Making something run more efficiently doesn't have to mean speeding it up - it can be used to make the game run at a smooth speed (syncing to display refresh and counting frames) instead of speeding up when there are less enemies and slowing down when there are more, or add other more complex elements to the game.
Personally I think somewhere between original Manic Miner's Central Cavern with music off (about 12fps) and the GBA version (20fps) is a good speed, which is why I set the default speed to 15fps in Redux.

Just for fun: if you collect the bottom item in Skylab Landing Bay while you're on 33 lives and *99xx points, you're killed by the extra life you're awarded for collecting the item.
MM-extralife_VP8.webm

Just for fun: if you collect the bottom item in Skylab Landing Bay while you're on 33 lives and *99xx points, you're killed by the extra life you're awarded for collecting the item.
MM-extralife_VP8.webm

By comparing Willy's sprite data with the attribute byte values assigned to the various block types in the cavern data, I've discovered a few effects that I think will arise within the Manic Miner game engine.
 
If you have more than 34 remaining lives and if the spare lives on the status bar are set to their rightmost frame of animation.  Willy's back foot in that frame has a byte value of #03, which matches a couple of magenta INK on black PAPER blocks in the game:
- In 'Abandoned Uranium Workings', some of the errant blocks (in 'even' columns) across the middle of the cavern will act as conveyor cells (no animation, but they will drag Willy rightwards).  This effect could be quite erratic if the in-game music is left on, meaning that the spare lives pass through that animation frame and the conveyor effect periodically stops and starts.  This should affect the new platform directly underneath the cavern's sole crumbly platform - that is in fact the very same new platform which led @DigitalDuck to improve his score here, which gave rise to this discussion!  N.B. No POKE is needed to observe this effect - just set the remaining lives to the appropriate frame;
- In 'Return of the Alien Kong Beast', the mid-height Water cell platform patrolled by the right-most 'rolling rock' guardian will, in theory, become crumbly.  Unfortunately, Willy can't access that part of the cavern to stand on that platform and cause its pixels to crumble away, because of the aforementioned blockage on the left-hand side of the cavern (as pointed out by DigitalDuck).  There is a single-cell platform occupying the same character row towards the left of the cavern (just below/to the right of the leftmost banana item), which is reachable during game play, but unfortunately that block sits in an 'odd' column, so the overwritten attribute (corresponding to a different part of Willy's sprite) doesn't match the crumbly cell attribute, and so no crumbling of pixels will occur if Willy stands on it even if it has been corrupted by a rogue attribute.  However, if that platform were extended by one more block (either left or right will do the trick), then the new extension to that platform would crumble when stood upon: POKE #DD02,#43 or POKE #DD04,#43 (in decimal: POKE 56578,67 or POKE 56580,67) - apply before entering the cavern.
 
Meanwhile, if you have 36 or more remaining lives and if the spare lives on the status bar are set to either their second or third frame of animation, then I believe the attribute value #06 (corresponding to the next pixel-row up in Willy's sprite) will be written across alternate cells of the top character row of the caverns.  This could also have gameplay consequences:
- The value #06 is assigned in 'The Menagerie' to an (unused) Fire cell type (the yellow bush that is encountered in other caverns), so as the number of extra lives continue to tally up, the top three items will be either embedded in or sandwiched between Fire cells, making them uncollectable without being killed (unless you move the animation of the remaining lives on to the first or last frame);
- Similarly, 'Processing Plant' would be incompletable once the errant Fire blocks reach across to the portal (and probably before that - I don't think it's safe to drop down from the starting point in the cavern without first making a jump that means Willy's head passes through the top character row);
- And the route options in 'The Warehouse' would be more restricted (for instance, you couldn't jump over the first Fire cell to Willy's right upon entering the cavern, without hitting one of the newly-created overhead Fire cells).
 
P.S. Whilst researching this post, I discovered for the first time that Matthew's original design for 'The Sixteenth Cavern' may have incorporated a switch!? (The switch graphic from the Kong caverns is present, unused, in the 16th cavern data.)

So I have a couple of corrections to this, namely that I'd missed some things that reduce the life count before some levels become incompletable:
Eugene's Lair - at 39 lives, the platform with the black toilet is completely overshadowed by the garbage platform. Unfortunately it's now one cell too high to safely drop down from, and there's no other way down without falling too far.
Return of the Alien Kong Beast - at 37 lives, all ways back down are blocked, and again the only way to get down is to fall too far.
Attack of the Mutant Telephones - while it's possible to go from top to bottom by jumping through the top of the screen, the platform in the middle becomes an island once you reach 42 lives and there's no way to get up or down from it.
 
Interesting. I'll post about it in that thread if I decide to experiment with that, but it's definitely unique for JSW-style games.

Yes, it's both the playing area and the buffer that's overwritten. When drawing a sprite it adds 256 to the memory address to go to the next pixel row, but naturally the screen attributes follow directly after the screen pixels so they're being drawn to. Even in the most extreme scenario lives are only drawn to pages 80-95 (memory addresses 0x5000 to 0x5FFF) which contain the lower third pixel data for the screen, attribute data for the screen, and the attribute buffers. I'm not sure where the stack is stored, but I don't think it's being overwritten here.

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).

Absolutely - unfortunately this scenario doesn't seem to exist in the vanilla game, but with the right sprites and colours you could have a situation where it cycles between floor, wall, air, and nasty (or the four elements, water, earth, air, and fire), and require the Willy life sprite to be in a certain state to make the level passable (perhaps even requiring floor at some points, air at others, and wall at yet others, so you have to "edit" the level as you play).

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).

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.

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

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.

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

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

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.

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.

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.

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.

Sounds like a great idea for another game...

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