Level 17 "Tunnel Scenario": 4 trapdoors with 2 lemmings each. The required strategy quickly becomes apparent, but there's a problem: the mineshaft going down to rescue the bottom left group leaves too high a step, so a kink is needed to lower its bottom part. From the skills provided I thought that the 'Basher-Blocker cancel' trick may be the intended solution, but I could not get this to work so tried a 'Miner-Blocker-Miner cancel' trick instead. This did work, but then I realised the Blocker was not needed. So my solution has skills to spare.
Level 18 "Stairway To Heaven": another breather level, prior to tackling 'Decimation.' I looked at various ways of separating out 1 or 2 advance lemmings before deciding the simplest way was the best – insert and then remove a Blocker. The provision of 2 Climbers led me astray until I worked out that I was better off using just 1. But overall not too difficult.
Level 20 "Havoc Highway": a level of 2 halves. In the first half the challenge is to advance the pioneer lemming while evading the zombies, and preventing them from following the pioneer's path, without using too many skills. In the second half the challenge is to reach all 9 buttons needed to unlock the exit. I kept on running out of Miners because I was being inefficient in evading one obstacle. My solution uses every Miner but has Builders and Shimmiers – and plenty of time - to spare.

Level 1 "Jungle Speedway": the chameleon trap by the exit means the crowd have to be compressed very tightly. I have several skills unused, but that does not necessarily indicate a backroute..
Level 2 "Sfift Action Freeway": I tried 2 routes, coming up 1 skill short with both. A 3rd route I'd been considering from the start looked impossible to execute, but then I realised that using one of MASTER-88's favourite tricks would make it easy to achieve the necessary synchronisation between the advance lemming and another. There are several viable variants to my solution – for example, in two variants I don't clone the Disarmer, and in one of these I save 100 rather than the required 99.
Level 3 "Lethal Sidewalk": a relatively straightforward level, with very generous time limit.
Level 4 "You Have To Take Little Detour": I had 1 false start with this. You need to know one Stoner trick and be very precise with positioning and timing.
Level 5 "Minute Mile": mind-boggling. The key challenge here, besides the super-tight time limit, is how to get past 2 obstacles while sacrificing only 1 lemming, since 1 has to be sacrificed by the trapdoor. There is no way past the 1-way pole without using a Stoner or a Bomber. This means the Flipper has to be passed without losing a lemming. I looked at various Blocker-Flipper interactions, but none of them quite worked, within the time limit – leaving me with several ways of rescuing 77 lemmings, but not the required 78. Eventually I realised it was possible to free up a skill and use it in a weird way that indirectly allowed the Blocker-Flipper interaction to deliver as required. If this is the intended solution, the level design is so ingenious.
Level 6 "Demolition in Coalmines": this is a large and long level, with a 15 minute time allowance. It is very difficult to free the crowd without using too many skills. I considered freeing them from below, using the sole Basher to go underneath the trapdoor chamber; but this route faces major problems with the chains and firebreaks. My solution, by using spare skills to reduce delays, takes well under 10 minutes.
Level 7 "Lemmings in Slaughter House": at first glance this does not appear extremely difficult. There are 2 Shimmiers to help get the advance lemming to where it needs to be to forge a path for the crowd. But then you realise there's a major problem with the group on the right: 2 traps to disarm, plus a high release rate, spell trouble. Solving this headache needs lateral thinking and experimentation. Another challenging puzzle.
Level 8 "Bullet Train Lemmings": another great challenge. I looked for a way to shift the first lemming from the front of the crowd, where it has to be to disarm the first trap, to the back - to give it ample time to disarm 2 traps and mine to the exit. I think this is essential to any solution. There are some spare skills that, as far as I can see, cannot be used.
Level 11 "Lemmings On Thin Ice": a much needed breather level, where it is not too difficult to beat the save requirement and save all 80. The time limit is very generous.
Level 13 "Very Tricky Position": this needs precise positioning of the Builders, which took me several attempts; and some very difficult work at the end, using the same trick as in level 15 of the 4th rank.  I don't see why the time limit is twice what it needs to be – maybe an element of misdirection?
Level 14 "High Place Expresslane": the key to this level is finding a mining route that is economical on Builders; and the key to that is where the Bashers are deployed. Working this out is challenging, but once that has been achieved it's not too difficult to meet – and exceed – the requirements for the 2 Talismans.

Thanks for the tip. I had heard of the Blocker Basher cancel trick, but not seen it in action. That left me having to choose between using the Shimmier in the right place or using it to cancel the Basher.

Level 8 "Lemmings Are Grounded": not yet solved. I am assuming that the solution involves an advance lemming going along the top, mining to the right and then being turned by a Blocker which climbs up the wall, then a Basher to free the Blocker & get the group to the exit.
Level 9 "All Stepping Stones Don't Help": I had problems with this because of a false assumption on my part. I thought that Sliders would splat if they descended from a platform, where the distance from the underside of the platform to the landing ground is 3 pixels more than the distance from the bottom of the splat ruler to the pink mark. But they don't - even when the Slider's lower foot (in the final frame before it transitions to a faller) is 1 pixel higher than the pink mark, with the splat ruler anchored on the ground. Once I realised this – thanks to a sneak preview of part of Master88's solution – it just needed some experimentation to find a solution. As Master88 says, there is more than one possible solution.

Level 11 "Turbo Tunnel": this level is all about meeting the time limit. A trial run shows that it is not possible for the last lemmings to reach the lower exit within the time limit. From this it follows that they must aim for the other exit; and this dictates how 3 of the skills must be assigned. The remaining challenge is to ensure that those lemmings that are reversed while obstacles are being removed are themselves halted and re-reversed in good time. Timing is very tight – I had less than a second to spare – but there is ample scope for tweaking the timing and positioning of the manoeuvre that delivers the re-reversing in good time. 
Level 12 "Season Of Miners": I found it relatively straightforward to save all but 1 lemmings. The problem arises at the end, where advance lemmings - that mine back away from the exit - have to be halted and reversed. It took me some time to find a workable option for removing the Blocker – requiring careful attention to detail to economise on miners. Timing not so tight here.
Level 13 "Walking On Hot Coals": an amazingly easy level, solved with quite a few skills to spare. Presumably a backroute.
Level 14 "Methods Of Masters": not yet solved. It is easy to see where the Cloner should be used to help create a route for a Basher to get through both central blocks – but very difficult to implement.
Level 15 "Final Trick": another level where you can easily fall 1 short of the save requirement. Looks like it needs a clever trick with the 2 Platformers, but I don't know a trick that helps here.
Level 16 "There is No Time To Waste": looks impossible within the time limit. The Digger above the exit has to stop at a particular point: any sooner, the crowd will splat; any later, the Digger will exceed the time limit. This restricts options elsewhere. If this Digger is advanced by making it a HangGlider, it will miss the exit. Otherwise, the crowd have to be compressed and then released so they reach the above-exit Digger just as it is halted, to avoid the crowd either splatting or exceeding the time limit. The best I can do so far is to rescue 37 out of 40 using 5 skills, or (sacrificing the Digger/Glider) 38 using 7 skills.
Level 17 "Edge Of Steep Cliff": it took me a while to spot the obvious (or should-have-been-obvious) solution to the problem of how to hold back the crowd while advance lemming(s) prepare a landing ground. And then I could not get the 'reverse a Builder by building just beyond another' trick to work so had to find another approach. Ended up comfortably within the time limit and with plenty of Builders to spare.
Level 18 "Puzzle Of Pharoahs": getting the group on the right to the exit is fairly simple, but it's more complicated for the left group. There are Miners and Blockers to spare, but careful thought is needed for where to use the Builders. The time limit is not an issue here.
Level 19 "Polar Night": At my first attempt I ran out of Miners and Platformers way too soon – partly because there was one obstacle that seemed to need quite a few of these. But there is a way round that. One advance lemming has to do all the work. And with one of the two groups you have to sacrifice some skills to allow its release only after a delay.
Level 20 "Hour Glass": a Zombie level with only 2 active lemmings, but the key challenge is to reach all 11 buttons – 1 guarded by the Zombie – before the Neutrals arrive at the exit. This is really tough. On the left, 6 buttons make for 720 possible sequences; on the right, 5 buttons and the Zombie guard on one make for 360. Many of these can be ruled out immediately, but that still leaves quite a few potentially viable options. Timing is fairly tight, as is the supply of Builders, so every effort is needed to economise on both; and the zombie climber/floater needs to be removed from the scene. A nice challenge to finish the rank with, though I reckon level 16 is harder.

Level 1 "Rush Hours": a very difficult level to start off with. Needs knowledge of several tricks, some familiar to most NeoLemmix players, others less well known. I wasted some time with complicated manoeuvres at the bottom left before realising there was a simpler approach, and realising the importance of the web. I did not even think of trying for the talisman – managed to save the required 63 but needed 1 more minute and 3 more Miners than the limits set for the talisman.
Level 2 "Go Around Inferno": a much easier level. It's obvious where the Cloner has to be used. The challenge is to get through the obstacles using only 2 Bombers – this needed experimentation with the release rate and careful use of Climber.
Level 3 "Don't Let Walls Stop You": this needed a lot of thought and to work out how to save a Bomber, as it looks like you really need 3 or 4 but have only 2. In the end I turned to Master88's Miner-Cloner-Bomber trick – see https://www.lemmingsforums.net/index.php?topic=6303.75 post #77.
Level 4 "Climbers Escape shaft": another relatively easy level, even to unlock the talisman. The main challenge is to ensure that the brick to seal a gap is laid after the entire crowd have climbed past it but before they fall back down.
Level 5 "Offer a Helping Hand": it did not take too long to figure out the main elements of the required strategy. But it's the difficulty of execution that puts the level in this rank. The only way to access the exit is by using Builder plus Blocker, which obviously needs good synchronisation; but the two lemmings involved also have to be well synchronised for an earlier trick, and this leaves little opportunity for slightly advancing or delaying one of them between the two synchronisations. The clever design of this level means you have to think carefully about: how to route the 1st lemming so the 2nd can loop until its partner is ready to join it; how to set up the 2nd & 3rd lemmings so you can fine-tune their release to within 1 or 2 frames; and how to get some flexibility in the timing and location of the first synchronisation so you can adjust the timing of the Blocker's arrival relative to that of the Builder.
Level 6 "Agoraphobia": not yet solved. As far as I can see, both Platformers – as well as both Builders and a Stacker – are needed to rescue the crowd from splatting. This means that no Platformer is available to get over the traps, so the advance lemmings need an alternative route – which I have not yet found.
Level 7 "Strained Atmoshphere": an attractive puzzle. Some elements of the solution are clear immediately, but it took me a while to see where to deploy the Cloner and Shimmiers. In the end I was able to save 1 more than the requirement.   
Level 8 "Lemmings Are Grounded": not yet solved. I have not spent a lot of time on this, but at first sight it looks like more of each skill are needed. I am assuming that the solution involves an advance lemming going along the top, mining to the right and then being turned by a Blocker.
Level 9 "All Stepping Stones Don't Help": not yet solved. The title says it all. Besides the usual challenges, there are 2 problems I can't see a solution to. First, the top right 'stepping stone' has to be removed so lemmings can slide down the wall, but the Digger cannot slide, it just splats, even if I dig after reversing. Second, how to avoid the 3 non-climbers getting trapped in the trough to the left of the exit – the only solution I can see involves sacrificing 1 lemming, but all have to be saved.
Level 10 "Sky Bridge": I particularly enjoyed this puzzle. The biggest challenge is to combine compressing the group with reversing an advance lemming so it can build a bridge for fallers. After initially falling 1 short, I managed to save 1 more than the requirement.

Level 1 "Room of Levitation": this caused me a lot of trouble. Platform from the bottom, climb and shimmy at the far right, then dig and somehow find a way to get the group up to the exit? Or platform from the top and get over the traps? And how to hold back the masses without using too many skills? My solution to the second issue uses 2 Shimmiers and 2 Stoners; and leaves 3 skills spare, so maybe it's a backroute.
Level 2 "Deep Dark Mineshaft": with so few skills and options available, it should be easy to find the solution by a process of elimination. But the second advance lemming has to be timed just right to reverse the first and get in the right place for a faller from the stone to Bomb the trap without removing too much of the bridge.
Level 3 "Windy Well": A way down is needed for those lemmings from the top trapdoor. But with only 1 Miner, and no Blockers, most of the work has to come from below. There are 2 challenges here. One lemming from the bottom trapdoor has to be really economical in its use of Fencers and Stackers. And at the top, the bridging needed for all but the first 5 spawners prevents the early ones from reaching the shaft, which calls for an alternative way of getting them home.
Level 4 "Diamond Mine": the challenge here is to get 2 Climbers close together – but not too close – so one can be made a Stoner which becomes a platform for the other. The set-up makes this tricky to achieve within the time limit. I ended up with 8 seconds to spare.
Level 5 "Diabolical Run": a breather level. Trial and error identified which lemming had to be made the Digger so that the first could advance well ahead of the others.
Level 6 "Under The earth": this was tough. I thought I'd found a clever Builder-Stoner-Shimmier-Slider trick with the advance lemming, but then realised that being a Slider took that lemming to its doom. So it had to be repurposed and the trick replaced by something simpler.
Level 7 "Sacfrife": it took me a while to ensure that, of the lemmings rescued from the left pit, not a single one goes off to its doom on the left. In the end the solution was easier than I expected. BTW, not sure what the title means – Sacrifice?
Level 8 "Triple Trouble": skills to spare here. Initially I over-complicated things looking for a clever way of rescuing the bottom lemming that can't be made a Swimmer, when actually there is a simple way.
Level 9 "Rampage In Fossil Canyon": a level I struggled with. It's easy to save all but the Blocker, and set up the Blocker to head in the right direction once released. But saving the Blocker needs 4 of the 8 terrain-removing skills, and a Basher is also needed at the top. That leaves only 3 terrain-removing skills to get the crowd up to the bridge; frame-perfect precision and a bit of lateral thinking are needed for this.
Level 10 "ACT FAST!": relatively simple. I managed to save 1 more than the requirement, with a massive 0.24 seconds to spare.
Level 11 "Capital City Web Ville": I usually struggle with webs. This time, I had to decide whether to use one of the Shimmiers to halt a Miner, or use it to follow the first advance lemming – which turned out to be the right option. The Sliders come into play by allowing the advance pair to Bomb in exactly the right places. Then Miners or Diggers are used on the left side of the web to allow a handful to reach the right side where they can help free the group. Once this is worked out, it is straightforward to save 76 and get the talisman. And with a different approach to containing the crowd at the start, 77 can be saved.
Level 12 "Mole Miles": another breather level, and easy to get the talisman.
Level 13 "Extra Steps is Accetable": options are limited here, so it does not take too long to rule out some options and find the one that works.
Level 14 "Meeting Point": by far the most annoying level of the rank, for me. The strategy is clear, but the execution very difficult, with one Digger having to be cancelled by another, timed so the pit is deep enough that the 4th lemming cannot go to the right but not so deep that the crowd falls into the water. It took me ages to find the right combination of release rates, Digger selection and location, and Platformer timing. Though at least there was scope for some calculations to find the combination. Later on, a Basher-Platformer from the right and Basher from the left have to be synchronised perfectly, and this is purely hit and miss – the Platformer's final tile kept on being removed by the Basher from the left, even after that Basher had finished and become a Walker; why is a mystery.
Level 15 "Lagoon of Erruption": it took me a while to decide what route was best for the lemmings on the right. For those on the left, the issue was how to release 3 advance lemmings, suitably timed.
Level 16 "Boiling Climb": I enjoyed this level. Stoners have to be used in 4 different ways: to contain; to reverse, with a Slider; to redirect a Shimmier; and to bridge a gap.
Level 17 "Lemmings Dream Wonderland": another example of the required strategy being clear – because no alternative could be viable – but the execution difficult. It took me ages to achieve the pixel-perfect precision needed for this.
Level 18 "Rules of Freefall": as with quite a few of Master-88's levels, it pays to look very closely at the terrain. The Builder does more than just bridge the gap. I did not find a use for the Climber.
Level 19 "Hot As Loaf": another tough one, as you'd expect from the rank position. The first challenge was how to use the Slider and Shimmiers economically, via the Cloners, to forge an advance path. The second was to ensure the crowd all head left on exiting the shaft – easy enough to arrange with a Builder over the shaft so they can only enter the shaft from the right, but not so easy when that Builder is needed elsewhere.
Level 20 "Frigit Crusade": an enjoyable challenge to finish the rank. Also a very honest puzzle in the sense that the skills provided, plus careful consideration of the opportunity provided by the terrain, lead you to the solution, enabled by precise timing of Shimmiers exiting the pit.

If a Blocker is used to get the lemmings to the top, how can it be saved? I have found a way to get the Blocker heading in the right direction when released – but I need 4 skills to release it, which is too many. Using just a Miner to try to reach the Blocker means the rescuer lands to the left of the Blocker; so I need Miner-Digger to land on the Blocker, then Digger-Basher to release it and save the rescuer. 

Level 2 "Gorge":  a very easy level.
Level 3 "Fiery Cavern": a straightforward level, with one advance lemming forging a path for both groups, while one group is held back, before they join up.
Level 4 "Path of Fire Twins": shows the advantages and disadvantages of Sliders. Needed a bit of tweaking to rescue all the Blockers, but not too difficult.
Level 5 "Frozen Pass": unless my solution is a backroute, some of the skills provided are red herrings. You need to know how to create an upwards path with Bashers, Miners and Builders.
Level 6 "Room of Shredder Traps": a step up in difficulty. 1 advance lemming needs to create a path for the others. That part is straightforward, but releasing a second advance one, some time after the first, is a challenge; the Slider plays a vital role. The solution needs perfect placement, both early on and near the end.
Level 7 "Swastika": Equally difficult. From the bottom trapdoors, the first lemming does the advance work; from the top trapdoor, the last does the key work. I had quite a few false starts with different ways of delaying the second lemming at the bottom left – most of which left problems elsewhere. One of my solutions uses the Stacker to delay; the other uses the Stacker in the obvious place, with a Miner doing the delaying.
Level 8 "SnowLem Land": a breather level. Needs the Blocker to turn a Builder, and careful attention to the topography to rescue the non-Climber from the right-hand group.   
Level 9 "Hard as Steel": an easier puzzle, but still needs a bit of figuring out to ensure that the 1 of 5 lemmings that cannot be made a Climber is delayed until a rescue platform is in place. In fact, only 1 Climber and 1 Miner are needed.
Level 10 "This Puzzle is Crystal Clear": I hate spider's webs, but even so it was not too difficult to save 99. However, care is needed to avoid the Hang Glider overshooting the exit. First I found a complicated solution, with the advance lemming bashing back to free the group, where I had to: time things so that the first lemming liberated by the advance one is the 100th spawner, which is only slightly ahead of the 1st (which follows close behind after looping round); increase the distance between 100th and 1st so that the 100th can be sufficiently advanced in its mining so that the early followers do not simply walk past the mineshaft; and save the Hang Glider, while still allowing the later lemmings to avoid the trap. Precise timing is the key to the first challenge. The spare Climber/Floater can help with the second. For the third challenge, a sneaky bit of pretend mining did the trick. But then I realised there is a simpler solution, which leaves 3 spare skills.
Level 11 "Center Point": Timing is very tight here. The first Stoner has to go in the middle. The second Climber is used only after the middle is reached.

With only 1 of 100 lemmings to be saved, and only 2 Bombers to get through 3 pit floors, a Nuke solution is clearly needed. So the final 2 lemmings have to reach the exit area before they explode, but they cannot access it until an earlier spawner has exploded. If I understand the game mechanics correctly, the time interval between the first and last explosions depends on how many lemmings there are between them, still alive at the point of Nuking. This creates a problem: if there are too many exploding lemmings, the ground at the bottom is blown away. So how to avoid this while still keeping most of the lemmings in play? I used a Builder and Blocker to corral the group to the right of the middle pit, while allowing the first spawner to escape. Timings and release rates have to be handled carefully. My final 2 lemmings were not tight together when approaching the pre-exit trap, but fortunately the trap is relatively generous.

Level 13 "Failed Hibernation": the traps are so rapid-fire that, for 1 of 5 Climbers to pass the 4 traps, the 5 need to be so tightly bunched that they appear on screen as a single lemming. Even this may not be enough, with the chameleon traps firing every 5 frames – far faster than a pair of Climbers can get through these traps. This made me think that bunching up the lemmings between a pit wall and a Stoner would not work. Eventually I realised that it's OK for each chameleon to gobble 2 lemmings; and that making the gap between a Stoner and a pit wall as narrow as possible is not a good idea. Needs perfect placement and timing, but a nice puzzle.
Level 14 "Salvage Operation": another challenging level. One key element for my solution is making sure that, when the group are freed, the first lemming to advance is a singleton, not one of the pairs.
Level 15 "Arrows": a breather level. Lemmings from the middle group free the left and right groups. I got the gold talisman on my second attempt.
Level 17 "Castle Conqueror": a good challenge, a large part of which is how to delay most lemmings while facilitating the necessary advance bridging. The 3 Shimmiers are used in 3 different ways, one of them a variant of a trick learnt in the first level.
Level 18 "Hall of Hope": not difficult to meet the save requirement and time limit, but my first attempt to do better ran into problems with running out of Platformers and using more Bombers than I wanted to. What was needed was an economical way of releasing at least 3 advance lemmings: the generous Climber allowance suggested a setup that allowed only Climbers to advance. Eventually I was able to save 74 lemmings (the requirement is 70) in a reasonable time.
Level 19 "Hydroelectric Powerplant": I learnt a new trick here, making a stack ascendable by using a Fencer, some distance away, to make a notch in the middle. Not too difficult if the skills are used frugally, and another generous time limit.
Level 20 "Watch Left And Right": an easy level to finish the rank, with lemmings from the right-hand trapdoor doing most of the work.

Simple use of Builders would leave the top of the bridge 3 pixels too low. So I would like to use a Shimmier with each of the first 3 Builders, and one at the end to stop it reversing. But there are not enough Shimmiers to allow this. So the final Builder reverses and has to be turned around, which costs me 9 seconds; and I miss the time limit by 4 seconds. Ideally the final Builder would be left with enough horizontal room to finish without then reversing; but if I do that the bridge does not gain enough vertical height. Still trying to figure this out.

Here I have no idea how to tackle this. With a locked rapid release rate, I don't see any way to stop several of the early lemmings from falling into the water. Perhaps there is some clever trick with Stoners that I do not know.

Level 1 "Oh Yeah More Lemmings": an easy introduction. It was straightforward to get the silver talisman. I have not attempted the others.
Level 2 "Season Round":  a long but not too difficult level. Getting the bronze talisman needed some careful thought.
Level 3 "Adventure of Pharoahs": another straightforward level, with a very generous time allowance.
Level 4 "Exit towards End": more of a challenge, with some tricky sequences needed to get the talismans.
Level 5"Lemmings in firework factory": it took me a while to work out how to use Platformers in different places to keep the crowd safe.
Level 6 "Dockyard": a nice puzzle. It's possible to save 49, compared to the required 47.
Level 7 "A lot at once lemmings": I struggled more with this than any other level in this rank. Use the Bomber and the Basher in the obvious locations, or swap them around? If a Builder is needed to rescue fallers, how to get this facing towards the exit, so the Builder does not head off and drown? Could using the Bomber in a 3rd location solve this problem? Eventually I realised that making full and proper use of the Hang-Glider is the key – though the solution needs precise timing in the early part of the level. Once the correct strategy is found, getting the talisman is easy.
Level 8 "Bottom of the well": a surprisingly easy level, needing just over a quarter of the time allowance.    
Level 9 "Re Energize your lemmings": another entertaining puzzle, with one of the two lemmings helping to rescue the other. Time allowance not so overly generous here, but still ample.
Level 10 "Going Up Lemmings": completely different from most levels in this rank, in that the required strategy is obvious but execution has to be pixel-perfect and frame-perfect. I beat the time limit by a tiny 0.06 seconds.
Level 11 "Crystals Cliff": another breather level. Here I looked for a strategy not using Bombers, so all 50 lemmings could be saved.
Level 12 "Think Fast Disarmer": not too difficult but still an enjoyable puzzle. 
Level 13 "Winter Rush": one of the more difficult levels in this rank. Do you get 1 lemming to the end, reverse it and bash back all the way? Or try to get past all the obstacles with the small number of skills provided? Or go for a hybrid approach? I reckon only one of these 3 options is viable. 
Level 14 "Twins Parkour": another entertaining 2-lemming level. One lemming has to wait while the terrain is prepared, but the time limit is not massively tight.
Level 15 "Donuts Paradise": I suspect there several alternative solutions, though mine has only 1 Builder to spare.   
Level 16 "Create a Paths": this took me a while to solve, until I realised that using the first Cloner in the right place would remove the problem I was facing towards the end of the level.
Level 17 "Gem Cathedral": here the talisman solution was completely different from my first effort – and with so many Builders to spare, I used some to speed up the later lemmings. Using the Digger in the right place was vital.
Level 18 "Caution Walk Over Bridge": a quick but entertaining challenge. It took me a few minutes to see where to use the Shimmier, because originally I wrongly thought it would be needed elsewhere.
Level 19 "Clone Wisely": one of the easiest levels in this rank, if you pay attention to the title. 
Level 20 "Miners and some dynamites": lots of Miners and Builders needed here. There must be quicker solutions than mine, but again I wanted to minimise the use of Bombers.

Like Kaywhyn, I found Tricky 3 "Which Way, Mr Scarecrow" the most difficult level – it took me a long time. Each lemming has to navigate 3 bi-directional splitters to get home, so – even ignoring the Zombies - there are 8 potential paths, of which 2 need no intervention, 4 need one, and 2 need two. So 8 lemmings would need 8 skills, and 20 need 20 – which leaves only 5 skills free for evading Zombies. I suspect that is impossible, so some lemmings need to be helped by either a Zombie or an earlier lemming turning the scarecrow in the desired direction. I looked for a pattern with the first splitter encountered: alternate left and right, or alternate in groups of 2, 3 or 4? Unfortunately I tried 3 of these options before finding the one that worked. With the help of 92Dexter11's tip about turning lemmings around, I eventually found a solution that uses just 23 skills.

Treacherous 3 "Pumping Station" initially looked like one of those levels where the required strategy is clear but execution is time-consuming and tricky – having to send up a succession of perfectly-timed Climbers to make sure that later-spawning lemmings do not splat. But it turns out there is a solution that avoids any risk of these splatting and only needs 2 Climbers (maybe only 1, but that would make timing very tight).

Treacherous 6 "Pushing Up Daisies" is ingeniously designed and provides quite a challenge for the Talisman. But it's one of those levels where you can get close and then do some final tweaking to avoid running out of Platformers.

Treacherous 10 "Ring Of Fire": a nice challenge to end on. I was having trouble rescuing the lemming that acquires the Jumper pick-up without causing problems elsewhere, so I looked to see if there was a solution not requiring the Jumper. And there is.

Fun: early levels provide useful introduction/refresher for skills used later on. I found a couple of possible backroutes, for levels 10 'Laugh if you like lemmings' and 25 'Lemmings, lemmings not everywhere'.

Tricky: Backroutes for levels 6 'Lemming psychology' and 26 'She has a clever plan'; maybe also for a couple of other levels.

Taxing: I particularly liked the puzzle provided by level 11 'The ascending shimmier scenario,' where  my solution is a minor variant of the author's, which saves a lot of time; also 28 'Poor lemmings.'  The hardest level for me was 26 'Trouble times 3' where I found it very difficult to synchronise the timings. My solutions for quite a few levels may be backroutes – notably level 2 'Many traps about'; level 12 'On the Edge'; 15 'This is an AWESOME level;' 16 'Heights beware'; and 25 'Follow the boss.' For level 7 'Every lemming must think for himself,' my solution is faster but far less fun. Level 30 'We might all fall down' is another level where a slight tweak to the solution can save a lot of time.

1 Blue Works: a lengthy but relatively straightforward level, with what seems to be a major backroute available.
2 This room is boiling: the most difficult level in the pack, for me. There are so many possibilities as to where to deploy the Cloners, and it is tempting to use the first one too early. Also, I wasted a lot of time trying complicated ways of accessing a couple of the pick-ups, because I failed to spot the easier way. The Zombies on this level are a minor distraction that just delay the effective start.
3 Be a hero: I reckoned there was only one way to solve this within the deadline, but I was wrong – my solution differs from the author's.
4 The roads that cross: 3 sets of lemmings to be co-ordinated. There must be lots of different solutions here; mine is reasonably quick. Whichever one you go for, you have to be patient with those on the right – possibly even the advance party. 
5 Up and down!: again there must be quite a few solutions available, at least in relation to accessing the pickup skills and creating a path for the upper group. 
6 This way or that: a relatively easy level for this rank, as I could not see any alternative solutions, apart from minor tweaks. Timing is tight though. 
7 Separated poles: not too difficult a level; again I would think there are several alternative solutions possible.
8 Don't be a rotten egg: timings are tight again here, but there's still some scope for tweaking the start and exactly how the Cloners are used. 
9 The Pharoahs curse: this is a very long level, in space and time. 3 trapdoors, 3 exits, buttons and teleporters make it quite a saga.
10 Hercules'pillars: not quite as difficult as it looks at first sight, but still a considerable challenge. I looked for a route that did not use so many Stackers.
11 We mostly all fall down: a breather level. With a locked release rate, there's no chance of beating the time limit by much. 
12 The side too far: another long level, with the advance party doing all the work.
13 The lemming thief: a nice little puzzle – only 2 lemmings, but lots of buttons to be pressed.
14 The split pea soup: a range of paths available, but good co-ordination needed whichever one you choose.
15 The quicky food solution: a close study of the skills available allows you to work out what the solution must be – I doubt if there are any alternatives to the main part of the solution. I ended up with just a fraction of a second to spare.
16 Only a minute: another easy breather level.
17 Don't step on stones: a good variety of solutions possible here, and an interesting use of a cascade of splitters. I had to work hard to find a way of speeding up the final lemming, to stop it lagging a long way behind the others. It's possible to beat the time limit by nearly 2 minutes, though that solution is not very elegant.
18 Only 4 of them: a very difficult level. In the end I came up with a crude solution, which meets the 'Save' target with over 1 minute to spare, but feels like a bit of a cheat. However, one of the pleasures of the game is seeing how many different solutions there can often be to any particular challenge.
19 Up you go!: one of the less interesting levels – straightforward, lots of platforming and bridging.
20 Discolored lemmings: it took me a while to work out how to access the pickup skill embedded in the ceiling. The vast array of traps before the exit means that the group cannot be released early. It's obvious where the Cloner has to be used, but there is scope for varying exactly how the Shimmiers are used.
21 A lemming twist please: a frustrating start, as you have to wait ages for the Neutrals to collect pickup skills. After that, it's an interesting challenge to work out where to deploy the Cloners.
22 A Beast!!! of a level: a key part of the challenge here is reaching all the buttons required to open the exit – quite a bit of trial and error is needed, along with some tweaks to stop a couple of lemmings heading away from the exit.
23 Up we go!: a very cleverly designed layout. Some aspects of the puzzle are easy to figure out, but I really struggled to find a way of freeing the lower group without causing a problem elsewhere.
24 All in please: fairly easy to work out what has to be done, but the timing is very tight.
25 Have a nice night!: the location of the teleporters and pickup skills gives useful clues to deploying the Cloners, and other key aspects of a solution are relatively easy to work out. But there is still scope for finding a speedy solution.
26 Steel areas of K*****: a key aspect of the challenge here is working out how best to access all the buttons, and in what order. How you use the Jumpers is important. A lot of trial and error got me to a speedy solution.
27 Another minute: a very easy level – maybe more appropriate to the Tricky rank? 
28 Don't mind the step: another long level; a bit of time can be saved if you find a way to avoid the Platformers reversing each time they bridge a gap.
29 Save me once more: I love a well-designed Zombie level, where you have to figure out a way of containing and/or removing the Zombies. My first attempt involved holding them back at the 1-way tower, but I couldn't get the timings right. In the end I came up with a tighter containment, which looks like a backroute. 
30 Meet in the middle: a nice puzzle to finish on. I could have done without the long wait for the Neutral to collect vital pickup skills. The layout and skillsets allow you to work out exactly where the Cloners must be used. But you have to work out how to use the teleporters; and it took me a while to realise where the Stoner and Stackers have to be deployed.