The reverse levels challenge thread

[Minim]

Looks like the reverse levels idea is popular, so without further ado, I will start this challenge thread.
If you haven't got the reverse level pack don't worry. You can log in (or register) and download the packs here and here.

So here are the following questions:

1. How many levels can be solved in reverse?
2. If the level is impossible with the provided skill set, how many more skills would be required to make the level work?

I have set up a table based on the original set, the pack which I have worked on reversing first. Here's how the table will work:

1. If the level is possible, a 0 is added, implying that there are no additional skills required to solve it.
2. If a different number is shown, it shows how many more skills you would need to make the impossible level possible (for example if Fun 4 required a builder and a basher, then I would put a number 2 on the cell meaning that 2 additional skills are needed before the level can be solved.)
3. An asterisk means that the level is not possible at all, even if you have 99 of each skill, and a reason would be stated.

I hope I explained every part clearly. Enjoy the challenges!

 --------------------------------------------------------------------------------------------------
|Rating | 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 |
|-------|------------------------------------------------------------------------------------------|
|Fun    | 3  4  8  2  0  3  0  0  0  0  0  0 10  0  0  0  0  5  0  0  0  0  0  0  0  0  0  0  0  0 |
|Tricky | 0 10  0  0  0  0  0  0  0  0  0  0  0  0  3  1  5  4  0  0  0  0  1  0  0  0  0  0  0  0 |
|Taxing | 0  0  0  0  0  2  0  1  4  0  0  0  0  0  0  0  0  0 10  0  0  0  0  0  0  0  0  0  0 10 |
|Mayhem | 0  0  *  3  0  0  0  0  0  0 10  0  0  0  0  5  0  0  0  1  0  0  0 13  0  0  4  0 16  0 |
|-------|------------------------------------------------------------------------------------------|
|Tame   | 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0                               |
|Crazy  | 0  5  9  3  0  2  0  0  0  0  0  2 11  0  7  0  9  3  0  0                               |
|Wild   | 3  0  0  0  1  0  2  3  0  0  0  0  6  0  6  1  0  0  0  4                               |
|Wicked | 0  8  0  0  1  0 11  0  0  0  0  3  0  8  0  5  3  0  1  1                               |
|Havoc  | 0  1  3  0  2  0  0  0  2  0  0  0  0  0  0  0  5  0  0  7                               |
|-------|------------------------------------------------------------------------------------------|
|Frost  | 0  2  0 12  0 13  0  0  4  1  0  2  0  0  3  2                                           |
|Hail   | 0  0  0  0  0  7  0  0  0  0  0  3  2  0  0  9                                           |
|Flurry | 0  0  0  0  0  0  0 16  0  0  0  0  3  0  0  0                                           |
|Blitz  | 0  1  7  3  0  0  0  6  0  0 13  7  5  1  0 12                                           |
 --------------------------------------------------------------------------------------------------


*Time is too limited for this this level to be solvable.

With the default skillset our final results are:
+ 94 levels are possible in Original Lemmings. (78.3%)
+ 68 in Oh No More Lemmings (68%)
+ 41 in Holiday lemmings '94 and '93. (64.1%)

While many levels are possible with additional skills, only one level is confirmed impossible. If the time wasn't an issue, then this only level would be solvable with 8 additional skills. Well done everyone!

[Clam]

Here's Fun 18 with 5 added skills, 4 builders and 1 basher.

Also, Fun 5 can be done with the default skillset, as I posted here (now with replay )

[finlay]

Tricky 4 is definitely possible...

Also I completed Mayhem 18, 19 and 28. (posted a replay of 19 in the other thread because I'm quite proud of working out the tricky bomber timing )

And Tricky 24 (Tightrope City) is possible too. It should be doable at 100% with the same release-the-blocker-and-turn-him-around trick that you used for Fun 9, but I'm not very good at pulling that off. (basically, you do a two blocker trap with one directly underneath the entrance, and then once you've used 1 builder to go over the gap, you can release the blocker under the entrance, and then you can probably release the other one too or something, I dunno, it's easy to solve, anyway!)

And here's Tricky 25, which is non-trivial and therefore quite fun. I saved 70/80, which is a lot more than the "normal" solution going forwards, but I don't think you can save 100%...

Taxing 13 is also possible (replay on request) – I ended up saving the minimum 98%, though, because I couldn't be bothered working out how to release my blocker (I had run out of bashers, so I tried with a miner which didn't work, but maybe if I put the blocker higher up on a stalk it might that way)

I suspect Taxing 14 is probably possible, given that it's not a particularly hard builder level to begin with. I'm not sure I can be bothered trying it, though.

Taxing 16 is also possible (again, replay on request) – I did it for 97% and finished with literally no time to spare, though, because building up to the exit takes a bit of time and there is only 3 minutes on the clock (the original level had a bit of this but not to the same degree). That said, I could have comfortably exploded the blocker a wee bit before I actually did, so it's my fault really for making the timing so tight.

Taxing 22 is possible, although I don't know about 100%.
Taxing 23 is possible – same solution as the tricky level.
Taxing 24 is possible and not hugely difficult – I think there are a couple of possible ways of doing it.
Taxing 26 is possible. It might be mildly more difficult to get to the top exit, though. I haven't tried yet.
Taxing 27 is possible (just have to bomb down).
Taxing 28 is possible. I haven't ascertained whether it's possible on 100%, but I had a few skills left over, so it may well be (unlike the forwards level of course!)
Taxing 29 is possible. It's not as trivial as some of the others, though, as you have to build up to the mound on the left using the 5 builders, and then you need to climb up the last little bit in order to block and release. I've managed lose 2, and there's a replay if you want.

Taxing 30 is definitely impossible with the current skill set – I think all the We all fall downs will have the same extra skillset needed, but I'm not sure what that might be.

Mayhem 1 is possible. I dunno about 100% though, I did it with blockers for lose 2. There's an awkward bit when you're going down where you need a floater, and you could probably use an extra blocker and lose 1 more to make it less tedious, but I (having found Lemmix's skip-ten-seconds function, which makes building much less tedious!) built over to the exit and back again to make the drop safe.
Mayhem 2 is also possible, and again, the fact that the level has floaters comes in handy.

Mayhem 3 is definitely impossible with the current skillset. Given the time limit, I'm not sure if it will be possible with any skillset, to be honest. (With the Fun 24 skillset, I had to build to get up to the exit, which took quite a long time.)
Mayhem 4 is impossible, but can be made possible with 3 builders and 2 blockers. (same way I did Fun 25)

I'm pretty sure Mayhem 5 is impossible with only 5 builders, but feel free to prove me wrong here!

Mayhem 6 is possible, and fairly easy (just build through the gap).

Mayhem 7 seems to be impossible. I think there is a possible solution if you add a digger and a miner (I trapped the lemmings to the right of the entrance by digging down – this way a climber can get up, and later in the level you can dig+mine down to release the lemmings). However, there may be something I'm overlooking here. I'm not sure I know the "best" solution to the forwards level.

Mayhem 8 is possible, and not too hard.
Mayhem 9 is possible too. Not sure about 100%, I used the blocker. Should be possible though, because you can probably make a digger trap and there are plenty of skills left over.
Mayhem 10 is possible. It's quite fun as a multitasking level, too, and getting down from the Pillars is quite interesting, so it's a bit harder than the original overall. I managed a lose-4 solution – although I'm sure that's not the maximum, I'm not sure about 100% because I needed a blocker for the right entrance. (Also, what the hell is with Lemmix's entrance order? That confused me for a minute there when the lemming didn't come out of the correct trapdoor!)

Mayhem 11 is impossible, as we know.
Mayhem 12 looks impossible to me, or at least too difficult to attempt at 1 in the morning. However, I know that Clam can glitch through the wall, so that might be our best option here, if it's indeed possible.

I don't think Mayhem 13 is possible from a cursory glance over it.

Mayhem 14 is fairly symmetrical, so should be as possible from the right as it is from the left. I haven't attempted it, however.

Mayhem 15 is possible.

Mayhem 16... not even going to attempt it to know it's impossible.

Mayhem 17, again, is very symmetrical, and should be as possible from the right as from the left.

Mayhem 18 & 19 are possible.

Mayhem 20 is impossible; as impossible as Fun 4 was.
Mayhem 21 seems to be impossible from a cursory glance, but I think it might be possible with one extra basher.

And as I mentioned, it's about 1 in the morning here now, so I hope this has been of assistance. I'll let you guys finish the levels off and confirm the ones I'm not sure about.

[ccexplore]

(Also, what the hell is with Lemmix's entrance order? That confused me for a minute there when the lemming didn't come out of the correct trapdoor!)

Believe it or not, this is actually emulation for a bug in PC Lemmings.  The lemmings do come out in ABBA order for 2 entrances in that version.

This bug is fixed for PC ONML onwards (and Lemmix account for that as well), but unfortunately as a side effect, it exposed that (this is well-known) Lemmix is not handling 3-entrance ordering correctly for ONML and Xmas levels (4-entrance ordering is okay).  Although I think we might be okay for reversed levels, as I don't recall off top of my head any levels in ONML or Xmas that have 3 exits.

=========

This does remind me of one thing though:  for the few reversed levels that wound up with multiple entrances, we should canonicalize the entrance ordering.  I would propose that the relative object ordering be left as is.  This is reflected by the "index" property shown in Lemmix and LemEdit.  So if there are 3 exit objects A, B and C with indices 0, 3, 6, the resulting entrances in the reversed level would have A, B, and C in that order, and so the lemmings are released A, B, C, B, ....

This may already be the case in minimac's levels but I have to double check (I intend to do a full pass on them over the next day or so to fix any and all remaining mistakes).

[finlay]

I think that's right: the only level with 3 exits is Fun 23/Taxing 18 (and there are only 4 levels with multiple exits in L1 and ONML anyway).

The simplest way to convert the levels (and I don't know if minimac has done it this way) is presumably to take each individual object and change its object ID number, ie directly change an entrance into an exit or vice versa. (and then change its y-coordinate so that the exit is on the ground and the entrance is above the ground)

I think as long as we're being consistent about using the same level sets it's fine either way, really.

Anyway, I'd be interested in seeing ONML done too (I predict that fewer levels will be possible). I might have a go myself. But another day... seriously, I've got to stop staying up late on the internet! (it's now almost 3)

[Clam]

I looked through the first half of Mayhem, and found some improvements to finlay's (impressive ) late-night efforts:

Mayhem 4 can be done with 3 extra skills (1 blocker, 2 builders), by using the 'spare' bashers to stall some lemmings and prevent them falling off the level. With one less builder, I ended up about 10 lemmings short after using up all the bashers; I'm not seeing much room for improvement here.

Mayhem 5, 7 and 13 are all possible, thanks to some sliding magic.

Mayhem 12 can be done by going through the ceiling, remembering that the top part of the steel is useless at stopping bashers. My 'cursor-digging' solution to the original level depends on some steel cancelling from the exit-top piece (otherwise you can't get far enough through the steel), so that's not possible any more. However, this comes down to how you define 'swap the entrance and exit' - if you swapped the entrance and exit objects and left the top piece where it was, you could get through there, but I think it's sensible to move the exit top to the exit's new location.

As for Mayhem 3, I had a quick run at it and got a lemming to within about 2 seconds of the exit. I used the slow climbing-in-wall glitch instead of sliding, so I'm almost certain you can make up that time, and since there's some building required to get to the top, you have some time to organise the crowd. This is going to be a heck of a mission though, so I propose we leave this one til last

[Minim]

And as I mentioned, it's about 1 in the morning here now, so I hope this has been of assistance. I'll let you guys finish the levels off and confirm the ones I'm not sure about.

OK, I have taken a look at the last nine Mayhem levels, and found the following to be possible:

22 isn't too difficult.
23 is possible and it does involve a nice range of obstacles for you to go through.
24 is already impossible with just three bashers. It may work using the slider trick though, but you need 100% and with a 99 release rate, the problems get worse.
25 and 26 are levels I had no problems with.
28 I have done already, along with finlay, so we both confirmed that it's possible.
30 is so possible, it is FAR too easy for it's position considering there's a choice of exits.

[finlay]

You missed a couple of the alterations I suggested! In particular, Tricky 24 & 25 and Taxing 13 are definitely possible and Taxing 14 should be, but it's just a boring level that I can't be bothered playing through.

Mayhem 14 is also fairly easy (except one of the peas has a permissible landing zone of 4 pixels that just jut above the trigger area, and it's harder to accurately predict either where to start building in order to land there or where to dig in order that both your hero lemming and the crowd land on it); I just completed it now to check, anyway.

EDIT: I converted all the ONML levels. They're in the other thread.

[finlay]

Well, I can confirm for definite that all of the Tame levels are incredibly possible even when reversed. Some of them are now very easy (particularly ones like 13, which now requires no skills, or 20, which only requires one basher), while some are suddenly not difficult, but at least non-trivial, such as 5, 17 and 18. More building is required, of course, except in the levels like 13 and 20 which required it before (yes i know that strictly speaking only 1 builder is required for level 13 and none for 20, but normal-person solutions require 4 for both!)

Crazy 1, 5, 7, 8, 9 are possible.

Crazy 10 is possible because the trigger area for the water trap is slightly below a piece of rock in which the water is embedded. I'm sure it'd be possible to find another way, because there are a few skills left over. I've attached a screenshot.

Crazy 11 is possible, but it turns out that lemmings walk off the right hand edge of the level (while they bounce off the left hand edge of the level cf Crazy 19, Taxing 18), so you need to use a bunch of bridges to turn the lemmings around... I'm not nearly as good at this as the likes of cc, though.

Crazy 13 is possible, and made a lot easier because of direct drop (so it only needs a blocker to turn the lemmings round for instance). This is one of those places where you could make a case for moving the exit slightly, because I don't think that point is where the lemmings would land on the forwards level, but it's where the exit ended up by me not moving the X-coordinate of the object in the editor, so I'm going to keep it like that.

And finally from the Crazy set, Crazy 20 is possible.

I can also confirm Wild 9 & 10 as possible – Wild 10 has a convenient and easy direct drop solution, at least. It should be possible going all the way round too but I can't be bothered confirming that.

Some of the other early Wild levels are impossible ("You take the high road" is particularly frustrating because it looks like it should be possible but seems to require 2 extra builders – you can put that down as its total (Wild 7!)), and the others I just haven't attempted. I haven't attempted any levels later in the game than that.

[Minim]

As promised, I've done some Havoc levels, and I will eventually evaluate on the ones that haven't been done yet:

1 is possible, as long as you know where the hidden trap is...
4 took me a few tries to get it right, but I went underneath the terrain managing to bash two pixels away from ground zero. I managed to re-turn the lemmings back to the right by building on top of the gaps in the ceiling.
6 had me frustrated that it wasn't possible, all because there aren't enough builders for me to take the outside route. It would've been handy having the platform on the right though, as that could've helped the reverse solution.
7 and 8 aren't too difficult
10 is possible, and a lot easier in reverse than normal. I managed to get double the requirement.
11 looks impossible from a casual player's point of view, but if I had more builders, a ceiling route would've been viable.
12 is possible, as long as you place your builders correctly.
13-16 I had no problems, saved a lot of skills
18 is possible, and has a cool solution.
19 even though the lemmings were stuck, I still managed to get them out complete the level easily.

Let the last lemming dig when on the silver platform. Build over the gap. Dig 6 times then bash through the bricks. Build up to the exit. Meanwhile set a blocker next to silver pillar, and blow him up.

I'm amazed that I solved more than half of the Havoc levels.

[finlay]

Oh wow, I've only just noticed now while watching Clam's replays that Mayhem 5 has no flamethrower traps. I thought they'd been accidentally deleted... turns out I just really don't know what was kept and deleted from the DOS version of lemmings...

[Minim]

There are two Taxing levels that I am having trouble with: 8 and 19. On 8, I can't seem to turn the lemmings around even with plenty of skills. You still will need 100% for that. For 19, I can only go as low as 67 additional skills. Using 64 climbers, 1 blocker and 2 builders. I'm pretty sure there's a more efficient way, but as there are only 2 minutes, the climbing seems to be the only method that is viable. The other is the sliding trick, but I can't pull that off.

Edit: I managed to get 19 down to 26 additional skills (Only just in time though). I've found a third method of steep digging down the left wall, combined with building and blowing up the two bars above the entrance.

[DragonsLover]

How Taxing 8 is impossible? If it's the matter of turning the Lemmings around, then you could use Builder + Miner + Steel trick for that, but then, it would require A LOT of additionnal skills to add. And I "think" there's plenty of time.

[finlay]

On 8, here's what you have to do to have all the lemmings walking left. I have attached a demonstration replay, which is not an example of how to complete the level, but the rest should be simple if you want to give it a go. I gave the level 99 builders, blockers and diggers in order to experiment with them (the replay uses about 12 builders, 2 blockers and a digger, but give the level more than that just in case), and found that lemmings start bugging out when they get too close to the top of the screen – they're doing something I personally have never seen them do before, which is transitioning from a walker to a faller or something. There's a possibility that the bug only happens on Lemmix (it rings a bell. but I really don't know that much about the inner workings of Lemmings or Lemmix. it's just a bug I haven't seen before, and I don't have that much experience with DOS lemmings anyway!), but I don't really care about that at the moment. Basically, you keep hammering on the mouse when the builder is near the top of the screen; I think three times he'll stop building before he bugs out on the top of the screen; then if you do it correctly you can release him with a digger, and he'll walk back down the bridge without having damaged it (I couldn't work out the rule for it, but sometimes he dug through the bridge and I'd have to start again). When he or any other lemming walks back up they'll change direction. Then you can release a blocker that you've made on the metal platform.

The other option I considered was bashing through the top of the steel, but unfortunately the steel area is set a few pixels above the top of the steel, so this wasn't an option in the end. I'm not sure the builder+miner+steel trick will work if the steel area is set a few pixels above. (edit: just confirmed, and it doesn't!)

By the way, how did you solve We all fall down in the end? What skills did you add?

More editing: OK, I've solved Taxing 8 with 1 blocker, 1 digger, 23 builders and 9 bashers. Since the original provides no blockers or diggers and only 10 builders, that's a total of 15 extra. [It's possible that the totals of builders could be reduced – some of the builders I used were mainly to slow lemmings down so that they didn't die, though. Another option at the start would be a two blocker-trap – it wouldn't be too difficult to build on the left, block, and then later bash to release him. I've also just realised that I could have saved 3 builders by not building over the gaps in the balls and just bashing through the balls themselves (the way i did it is just how I learnt to solve the level when I was a kid, and old habits die hard!) 15 will do for now though!]

Even more editing: because you missed it before, Wild 7 should be 2 extra builders. I'm also not convinced that Havoc 17 is completely impossible – sure, those pesky traps are annoying, but you should be able to build over them if you have a bunch of extra builders.

[Clam]

Basically, you keep hammering on the mouse when the builder is near the top of the screen; I think three times he'll stop building before he bugs out on the top of the screen; then if you do it correctly you can release him with a digger, and he'll walk back down the bridge without having damaged it (I couldn't work out the rule for it, but sometimes he dug through the bridge and I'd have to start again).

Interesting, I haven't seen this one before. What seems to be happening is that the stuck lemming bobs up and down slightly (I have no idea why it does this), so if you assign the digger skill at the 'up' part of the cycle, it finds it has no terrain to dig at, and a digger assigned with no terrain in range transitions immediately to a faller.

Sadly (or rather fortunately, given the number of skills involved), none of this is necessary to solve the level. Here's Taxing 8 with just 1 blocker extra.