Stacker cancel : assign a stacker at the exact same place than a previous stacker, or than a currently working stacker. This way the last assigned stacker will cancel after trying to set one brick over the already existing stack, and most importantly he will turn around.
I used this to contain and compress the crowd at the beginning, and to prevent the last climber from climbing the stacks leading to the exit.

Prepare 7 Flower Power. I had a surprisingly hard time containing the crowd and pushing the button here. I must have used a very suboptimal method, but it worked in the end !

Prepare 10 Construction Function. Very nice design on this one. I had a fun time figuring out a route from those thin diagonal floors, and went via some small holes here and there.

Prepare 16 Caught In Liminal Space Great design again !  It reminds me of the game Castlevania : Symphony Of The Night, mainly on PS1 and Saturn consoles if anyone is familiar with the game. The whole game is set up in a giant castle you have to explore. And where you think you're finally done with it and beat the final boss comes a twist :

Spoiler

You have to go through the whole castle again but it is reversed upside down, opening whole new paths and ways to explore !

So yeah, having reversed elements in here reminded me of that tremendous game.

Nuisance 6 Mesmerizing 1st level by Armani, I was not even scared ! And it went smoothly 

Nuisance 7 Mirror World 2nd level by Armani, I was not even scared, and I should have been ! See discussion above.

Nuisance 8 Hoopin' on the groove line I had fun jumping here and there. A bit disappointed by the end part tbh. Maybe I backrouted it and the intended solution is somehow funnier ?

Nuisance 8 In The Rear With The Gear Not a very big fan of the level tbh. One quickly understands what needs to be done, and after that there is no thinking involved.  I salute the original idea and the beautiful design.
And most of all I salute the reference to that Sergent in the Full Metal Jacket movie, that very one who tells Joker he better stays "In The Rear With The Gear".
Now please make a level named "Lem has guts, and guts is enough".

Nuisance 14 Sugar Free Lemming Aid I spent so much time on this one ! For some reason I tried to used the downer tree branch. Must have realized sooner that this is not the correct way because it is hard to reach that is used up almost all my skills.

Nuisance 19 The Aquatic Ruins Very nice design again, where you have to let a lemming wander around and make the work in a very precise order and fashion. Making sure the crowd does not splat at the end was not that easy, maybe I missed something.

Nuisance 20 The Choosen One See discussion above, a real trip for my brain.

Calm rank

The Stumbling Block Sorry I did not try to save as many as I could here, just let my luck go and saved enough.

The needs of the few I had a hard time containing the crowd here, and ended up doing it under the chameleon. Certainly not optimal but it worked.

A Slight Detour It is worth noting that I played the pack backward : Panic->Tense->Calm. Dont ask me why, I just dont know. Maybe I like to end with easier levels.
In any case, this was consequently the 3rd time I solved this level, and with supposedly the easiest skillset. Remembering the other detour solutions, I thought "enough with the detour, this level title is just teasing me". So I just brute-forced my way to the exit, sorry 

Status Quo I love the design of this one, buccolic (is that an English word?) walk under the rain.
I love how that precise raindrop makes crossing the pond with builders painful : bridges end right in the raindrop, then you are forced to go up and splat !
Once again I just said "to hell with it" and went the whole bottom route. Sorry again 

Your Egg Is Cracking Once again the 3rd time I saw this level, playing backward. I tried my best to save 100% here but did not manage to save the 6th lemming from the splat at the beginning, my builder is some frame short no matter what I do. Anyone could save 100% here ?
I must also applaud the egg design, it fits very nicely in the Oh No Rock original style and this is a serious feat.

The Lemming Hair Dryer A level for the girls ! Love the electrical design, I could 100% with the upper route.

Follow Me! I found this one hard for its rank. At first I tried the upper route but did not have enough constructive skills. Turns out the bottom route works : building the many gaps actually allows to spread the lemmings apart and makes the final timing quite lenient.

Break The Cycle I recently quite fully understood the power of the so called "Dolly Dimple" bridge which allows to separate a worker from the crowd with bridges only. Applied it here and end up with an extra builder at the end.




Tense rank

Lucky Brick 3rd repeat of this level for me. Sorry I just cleared all of them with mostly the same technique each time. This is what happens when you start with the hardest one : you cannot unsee the solution you had the previous times.

Going Down I love this one ! The bridge technique I used here is also similar to a possible solution in the ONML Dolly Dimple level, which is one of my favorite level of all time considering how much time I spent stuck on it in the 90's.

Meet In The Middle Good level, my favorite of the 3 repeats, and among the favorites in this pack.
I had trouble with this one, again my fault because I was trying to more or less reproduce the solution I had for the Panic repeat of this level! It did not work though, and I scratched my head for a long time ... until I realized the level name gives the solution! 
How dumb of me not to see it, when I actually did the same in the Save One pack : give clues on how to solve in the level name!

Wait For Me! I must say I did not understand this one. The save requirement of 1 lemming out of the 2 is weird ? I just let one lemming die in the water and saved the other with the many skills available.
No idea how to save both though.

Panic rank

Lemming-Lime Soda Very good level, among my favorites in the pack!
I used one builder at the beginning to allow the pioneer to dive in the water and avoid splat. Then I went the bottom route to free the crowd. Pioneer died though, RIP.

Freezer Burn Mean level, poor Lemmings die after about 5 frames of living. I had a hard time getting to save them, and just enough builders to do so. I'd say my solution is not optimal, but it works.

The Serpent Biggest roadblock to me. I spend much time figuring out how to get up there, the compression solution did not occur quickly! After that and the idea of half turning in the serpent's eye, things were not that easy because one has to place the miners very carefully to be able to save the crowd and reach the exit.

Lemmings Replacement Theory Tough repeat of Calm 2. At first I though it was simple, until the first miner fell right before the central block, and all subsequent lemmings with him, of course!
I kind of quickly understood that the 2 losses would be 2 miners going to the left, the hardest part was to manage a half turn with a lem to the right of the central block.

Be The Girl You Wanna Be No real difficulty in the buccolic sunny grass. I may have once again forced things with basher + builder cancel thing.

Cave-Divers Builderless level, you know how to please kaywhyn.
Love how you have to use the ascending terrains to their full extent here. Also dont waste the destructive skill, because a quick count when you finally get to the upper floor may show that you dont have enough.
I was a bit frustrated that one cannot do 100% here though (or have I missed it : how to half turn w/o the blocker on the right side ?). Also some skill assignement are very precise.

A Death-Defying Stunt Tremendous level 
Many possibilies here but also many of them that do not work, so I had to experiment a lot. The way to save the 2 blockers was quite obvious, but it used a lot of builders. So one has to be extra careful with the other parts of the level that have to be done almost w/o builders. Special kudos to the way you neutralize the bottom left trap right before the exit, this one took me much time to figure out.

As kaywhyn said though, I'd also point out that if one puts the left blocker a bit too far to the left on the beginning platform, he may not see that several shimmier can be escaped from the crowd. When you think about it, those shimmier going over the blocker when they are so close to it are pretty counter-intuitive. Maybe just shifts the shimmiable curved piece a bit to the left, so that even if one puts the blocker at the very left edge of the starting platform, then shimmiers can still be escaped ?

The Four Horsemen Of The Apocalypse Nice level to end the pack.
I could see a solution, though it was hard to set up correctly : over the exit, I had to make a digger pit with 2 lems in it. When the digging is done, I could make one lem walk to the right toward the other lems waiting to be saved, and the other walk to the left to the exit.
This was pixel/frame precise, and quite fiddly to pull out. So I think this solution is not the intended.

I totally agree with you : it makes perfect sense that a shimmier can access a reversed exit like it happens here.
What lead me to think that it was not possible here, is that in CPM the exit trigger appears floating in the air, and not buried in the ground (well, ceiling in this case) like it usually does.
But then again this makes sense with the way the engine works : the feet of the Lemmings (precisely the red star under them visible in CPM) touches the trigger area when shimmiering, so all good !

1) Figure out how to push all those buttons. As I remember from a level in contest 33 by Icho, you have to build some of your own shimmiable ceilings here. Also use the slider correctly.

2) Seeing the strict save requirement of 18/20, and the 2 stoners available, realize that I need to save this button pusher ; save The Chosen One himself !
This was the hardest part for me as all my attempts before that used the single digger elsewhere to either contain/free the crowd or make a way. So I had to spare that digger to save the Chosen One and this is where 3) comes into place.

3) Release the climbers correctly at the beginning to contain/free the crowd correctly w/o using the digger and stacker. This was not that hard actually.

4) Have a heartattack when ready to finally dig-save the Chosen One with the other climber at the end : digging in a diagonal floor leaves that little pixel triangle that prevents climbers from climbing 
Then I spent 15 more minutes trying to find another place to extract the Chosen One from down here, no success. Then I saw this extra stacker and understood the unbelievable combo : stacker + climber + digger = save The Chosen One 

5) Have a last rush of tension when I saw that evil Armani put a flip down there, instead of a boring non climbable wall, so that the Chosen One has a limited amount of survival time before falling to its doom.
Fortunately my digger finished its pit some 20 frames before the Chosen One came back, and they could all go together to the exit. Oh Wow !

I could clear it with what looks like a backroute since I spare the shimmier skill. Then I looked at Dexter's solution who also states he has a backroute. His is quite similar to mine, except I use heavier timing things to make the left bunch of Lemmings turn around in time before splatting from the digger pit on the right side. Joining my solution if anyone is interested.

Looking at Dexter's solution I also noticed that he makes a pionner use the reversed exit with a shimmier skill, good job!
This never occured to me because the Clear Physics Mode shows me that the exit trigger is actually floating in the air, so seemingly not reachable from where Dexter reaches it. I'm joining a CPM screenshot where you can see the exit trigger floating in the air, and Dexter's lemming exiting while not going over this trigger.
So questions : is this a bug in the display ? Do all of you see the exit trigger floating in the air or is it just me ?

The Strange Relics Of Lemnos had to be done the other way around, always hard to see but it solves both problems of where to put the bridge, and not having to cancel that basher.

Your Ancient Crash Site solution is a marvel. Save a bridge by making bridges in an unnatural way at the beginning. This level is on par with Armani's best tricky designs, reminds me a lot of Underroot in the last contest.

Also 100% on Spring Break looks easy when you watch Ico do it. For some reason, I'm just not that good at seeing how to use multiple miners.