1 The Locked Room Mysteries - A nice start to the rank. I went for the talisman on this one by using the diggers to get through the one-way wall.

2 Unfriendly Neighbours - The talisman to this one was quite the challenge, as rescuing the lemming that lets the zombies free was surprisingly tricky! I ended up constructing a small holding area which I sealed off at the last second for my solution on this one. I wanted to try and use the wheel trap at the top initially, but couldn't find a way to work that with the talisman.

3 These lemmings and those lemmings - Tricky level! Allowing the climbers to still be able to get up the central pillar again took me a little while to spot with the way I approached this one. I liked the way the disamers released the climbers at the end though.

4 Crowd Control - Compressing the lemmings is the main difficulty on this one. I construced a fairly narrow holding area using a miner + basher combo repeatedly but that doesn't get close to the talisman which seems pretty hard. I guess that probably involves some RR manipulation?

5 Thick and Thin - A favourite of the rank. I really like the way you have to be careful with the builders near the end of the puzzle to not leave too many behind. The various bits of terrain in the middle provide a lot of different options for how you split up the workers too.

6 A Sorting Problem - A very nice idea with filtering out the different hatches into different exits. The main challenge I ran into was how to filter the swimmers from the floaters - The only behavioural differences betwen the crowd are that one bunch falls slower & the other can swim. Unsurprisingly, letting half the lemmings drown doesn't solve the level, so I opted for catching the floaters after the swimmers fell past.

7 The Big Dig - Certainly a bit of an easier level compared to the previous few.  My first attempt did fall 10 seconds short of the time limit so I needed to go back and optimise things a bit. I wonder if the time limit on this could be made more of a soft-limit by adding a higher lemming total?

8 Equivalent Exchange - Tricky level, the platformers really run out quickly on this one too. Working out how to get to the bottom left exit is a challenging part given the laserer skill is all you have. I wasn't able to find a solution that preserved enough platformers that had the two sides of the map cross over, but I did find one where each side solved on their own. I'm guessing this is probably not fully intended, given the title hints at at least some interaction between the two crowds.

9 Fun with Lasers - A great builderless level & surprisingly tricky - especially given how strong the laserer skill can be in places for opening up areas of the terrain from distance. I liked the detail of using sliders rather than floaters / gliders here. They add some additional complexity and care required, otherwise they can easily end up going the wrong way out of a laserer tunnel.

10 Escape from Zombie Island - A really nice level to finish off the rank. I really liked the tension between wanting to get rid of the zombies to make a worker area but needing to keep them around so the basher doesn't go into the exit. I couldn't find a nice way to handle the crowd of zombies near the exit without digging through the one-way wall, but on reflection maybe I could have set up the holding trap on that side of the exit?

1 Lemming Entanglement - This is an excellent level . I think this is probably the hardest of the 3 I've played so far. I ended up solving this one by thinking about the level in reverse and asking about if it could ever work if I: (1) built from right to left from any of the 3 junctions or (2) Use the teleporter to bring the crowd down. After ruling those out I was able to focus on the other possibility and spotted the trick with releasing blocker with the digger which unlocked the rest of the level.

2 No Matter Where You Came From - Another great difficult level, and the verticality makes a nice change. I was able to find the route down quite quickly but, the main bit of difficulty was optimising enough skills & working out how to create a filtering device for the swimmers & sliders similar to the one used at the top of the level. There probably is a cleaner way to do this than how I managed it, but hopefully I'm not too far off with this one.

3 Hold My Beer... - This one looked like it was going to be difficult from the preview screen, and it certainly was. I had quite a few ideas that either ended up a skill short or a lemming short. I included a replay with one of my closest failed solutions where I was missing one floater at the end. My solution probably brute forces a part of room 2 a bit to make sure all the lemmings came out the pit in the same way - I'm guessing there is a cleaner way to do this part by saving a miner elsewhere which I probably missed. Very nice puzzle

Retro 1 Nice first level to the pack - not too difficult but not a pushover either. The worker lemming (or rotten egg) needing to take the top-route rather than following the same path the rest of the lemming would take was a good detail.
Retro 2 Nice semi-open ended puzzle around containing the crowd. I was convinced a save-all solution was possible here, and eventually found something that worked using some blocker trickery at the start.
Retro 3 Good early level, saving the climber using a basher was a nice detail though the timing was a little tight on my solution.
Retro 4 Nice builderless level! By bumping up the RR I was able to save a 2 miners which I imagine are required to do a bit more crowd control if you don't do this.
Retro 5 A nice challenge to try and save as many as possible here with an open skillset. I managed a save 29/30 in the end but I tried for a while to get a save-all by using the builder + digger + builder trick to turn a lemming around, but couldn't quite connect back to basher tunnel without running out of skills to get back up.
Retro 6 Nice puzzle with two distinct workers meeting up - not too hard but satisfying to solve
Retro 7 Very nice idea with re-using have all the blockers get freed to become blockers a 2nd time. The terrain hints to place the blockers was a nice idea to reduce execution complexity on this one.
Retro 8 I like these sort of levels where it is about efficently solving a seemingly simple looking terrain area. It wouldn't surprise me if there more than one solution to this given the skillset and terrain shape, but I settled on an approach using two different digger pits.
Retro 9 I really liked the multiple workers interacting on this one, and the timing with the icicle was very satisfying when it just worked out
Retro 10 Very clean solution, and very clever. The top-left hatch was probably the area I wanted to build bridges with the most, but the solution cleverly requires patience with this hatch in particular. I really liked that no timing was needed in the solution to this level - I did initially think the solution might involve 6px steps around the bottom hatches and some clever timing, but those solutions all ran out of builders.
Retro 11 Another very good puzzle. I found this a little easier than 10 but that's probably because I spotted how to handle the bridge area quite quickly fortunately. Not using a blocker to turn the miner, which is the initial temptation for this level, was a nice twist.
Retro 12 This is a beatiful solution and probably going onto my LOTY list. There is some very nice subtlety to where you need to place the skills on this for it to work out, and when they are placed correctly everything clicks into place in a very satisfying way. An early solution I had that didn't quite work (but thought it might have been the trick) was to put a builder ontop of the walkway after the exit to turn the lems around - I was quite pleased with spotting this as I thought I had to the key to level, but nope.

Quartet 1 - This is a really nice solution with two workers. This one is quite an open ended level with quite a few solutions.
Quartet 2 - There are a couple of solutions to this one! When I was first making this level I solved it using a blocker and freeing it later and didn't realise the overhang trick until much later.
Quartet 3 - You did find a nice solution with the chain on the left for this one - the main solution here uses the digger on the red bricks.
Quartet 4 - Very nice solution! I liked the way you got through the tree-planet-thing in the middle. The name on this one is a bad pun given the rocky terrain at the start is roughly fish shaped.
Quartet 5 - This is not the intended way to get out of the penrose triangle but would make for a good talisman given it saves the climbers!
Quartet 6 - There are a lot of possible solutions to this one - I think i've seen a different solution from everybody who has shared a replay so far! Originally this level was going to involve dropping a lem onto a bridge to repeatedly do the dolly dimple trick, but that kept getting horribly backrouted so I ended up scrapping it and re-worked the level quite a few times.
Quartet 7 - This was one of the first levels I made in the pack & I'm happy the level managed to hold up against the ways of holding the crowd back at the start! I like the way you created the timing gap in this one - any solution that has the basher continue into the hill is good!
Quartet 8 - I'm a huge fan of builderless levels too - I've found there is nothing quite as intimidating as a late-rank builderless level though! I really enjoyed making this level, in fact probably this one & Q16 are my two favourite levels.
Quartet 9 - Sorry this one lead you down a frustating solution path, the intended solve on this one shouldn't require precise spacing/timing but I couldn't work out how to get rid of all timing based solutions on this one. I think the central trick on this level suffers from having 4 lemmings rather than a big crowd - the compression method with the blocker would be completely required if the level was designed around 40 lems. In general I spent quite a lot of time trying to rule out fiddly timing precision for this pack (hence the locked RR for all levels), but I found doing that + backroute fixing around 4 lemmings to be really hard! I will probably adjust the structure under the crane up a few pixels more to hint towards the intended solution some more though.
Quartet 10 - I liked that you used various levels of the bridge area on this one - this one was inteded to be a bit easier and open after the increase in difficulty of 8 &  9. The talisman on this one is quite a nice exta challenge, though I know you tend not to go after Talismans!
Quartet 11 - Nice solve - Your solution using the digger -> blocker to bounce the miner is intended, though as you said you can place things to have the 2nd climber free the blocker rather than needing the cancelling trick.
Quartet 12 - Great solution on this one to get the talisman! The planets here are indeed roughly based on our solar system though I took quite a bit of "creative license" and themed worlds around tilesets too. I guess we don't really have a bubble tileset planet & I can't imagine it would be the most habitable planet if we did!
Quartet 13 - The idea with holding the lemming with the blocker is really clever but sadly the first backroute (this level has had no end of them)! I think I might add a metal spoiler to each of the cars which should hopefully rule out the miner usage.
Quartet 14 - Nice solution! This is a level with quite a few solutions that all use blockers in some interesting way and your solution is good. I do wonder if this is possible without using the floater (if you had the pickup skill from the start), I never was able to quite make it work though...
Quartet 15 - I liked the way you juggled the two workers on this one. This wasn't the intended solution but saves exactly 2 and uses the skills in a clever way so would be acceptable. Having said that I have been undecided for a while about adding a OWW to part of that shelf which would stop this solution working. I'm probably going to add it in the next update because I am still a bit worried about that shelf hiding a save 3 backroute in some way.
Quartet 16 - Brilliant solve! This is was my favourite level to make & style in the pack. I've really liked playing/watching levels over the years that have 2 lemmings the few times I have seen them, so wanted to make a 2 lemming level too. The main solution handles the middle area a bit differently but your solve here is good - You might be interested in checking the replay for that one though as I think you will like the other way the middle area can be handled. I was a bit surprised that sign wasn't splat height but I don't think I'll be raising it - I might adjust the top to be a few px lower so it is a bit more obvious it the fall is safe.
Quartet 17 - It's really impressive you found the intended solution as quickly as you did! This was one of the levels I built by making an area of terrain and trying to solve it in an interesting way, it took me quite a while to find the interaction used here - but when I did I really wanted to build the rest of the level around it.
Quartet 18 - I liked the way you navigated across the terrain with the two workers on this one. As you said, this is very much an open ended and more chill level to finish things on. I built this one based on feedback from WillLem around having a few more open levels in the pack for variety, and I'm really happy I got this feedback. I'll strongly consider closing off future packs in this way too, as making this level at the end of a long development journey on the pack was really quite satisfying from a creators perspective too.

Extra 1 - Nice solution, there are quite a few ways to control/delay the crowd on this one. This was a 2nd rank level in aqualems I think, so any solution that doesn't trivialise it is a good solution.
Extra 2 - The way you released the crowd with the miner was nice on this one. Originally I wanted to require quite a specific solution on this one which would have made it far too hard for an intro level.
Extra 3 - Good solution! I was quite fond of the way the builder was used on this level, so prioritised trying to bring this into quartet.
Extra 4 - Intended solution! I thought it would be kind of fun to include something like this after all the other heavily decorated levels, as quite a few of them started very plain and unthemed.
Extra 5 - Intended solution. The trick on this one was originally part of the solution for Quartet 15 on the pan near the end - the idea was to have a builder place a step through the edge of the pan and cancel the digger with a blocker when the worker came back later. It turns out this was a massive over-complication on my part though, as you could always just dig first and build afterwards. When the trick wasn't required anymore I decided the tutorial didn't really need to be in the main rank anymore.
Extra 6 - This is very close to the solution I had for this one & like with the main rank version there are quite a few. The talisman solution is a bit of a backroute that really can't be fixed without the button - do check the replay if you are interested in it, as it was a rather large "damn" when I first saw it after spending ages decorating the level. In response to your question at the end, the middle section is indeed poker chips with the brick areas representing cards.
Extra 7 - This is a good solution - any solution that builds that bridge at the start is good. This level and it's earlier version have titles based on an area in The Outer Wilds, the 4 level in its own rank idea was also to tie into that reference too. This terrain setup was surprisingly flexible in terms of how many ways you could arrange things to make puzzles even with just the classic skills.

Quartet 5 - Added talisman based on solution by kaywhyn
Quartet 9 - Adjusted terrain to make intended solution a bit clearer
Quartet 13 - Added some metal to the cars & added some terrain near the exit to remove a backroute
Quartet 15 - Added a one way wall and an additional object to the shelf
Quartet 16 - Adjusted height of one of the signs to make an alternative solution more clear

total: 22531

ohno_brick: 4147
ohno_bubble: 2828
ohno_rock: 2675
ohno_snow: 1116
orig_crystal: 4587
orig_dirt: 661
orig_fire: 1565
orig_marble: 2104
orig_pillar: 1196
orig_sega: 275
sms_crystal: 289
sms_fire: 78 
sms_pillar: 16

l2_beach: 15 
l2_circus: 195
l2_egyptian: 1   
l2_highland: 50 
l2_medieval: 13 
l2_polar: 16 
l2_shadow: 704

Note these counts are taken as if all groups are fully expanded.