Aquarius 1 -
Game of the Century Wow, this is quite a hard level to start off the rank. I've played plenty of levels where the word "Lemmings" is spelled out in the terrain, and they have pretty much have all been challenging for the most part, but even they're nowhere near as hard as this!

As mentioned before, I decided to resolve v3.3 of the level, as the one in the LP is an outdated version due to how I forgot to redownload the pack before I recorded myself solving the level. Therefore, I think it's only fair that I do so. Even then, the LP should make it obvious how much I struggled with the level. v3.3's is even harder, I feel. Unfortunately, I think it's still a backroute, as I still don't use the climber pickup

However, let me say that it took me a really long time to make the solution work out. Timing the climbers so that they all make it through before they got blocked by the builder staircase, for example. In this way, it would save me a cancelling skill with a shimmier/jumper so that lemmings can still escape later, such as the miner at the very end. This was very frustrating to get to work, but again likely not intended, as the intended one is probably far easier and less fiddly than mine.
Aquarius 2 -
Overpopulation Another very hard one but quite a good one. I learned a new trick here, which is the interaction of a stoner and slider. This is the easiest way to contain a slider, as they're stuck in an infinite loop due to the small holes on either side. In other words, it's almost the same as containing sliders with a stacker, except for the stacker you need to spend at least one skill to achieve the same thing. I believe the easiest would be mining and cloning it. For this level, I especially love the shimmier/bomber trick at the very end to blow through both floors so that the sliders can fall through without sliding and going out in the wrong direction. I think the funny thing was that I tried stretching out the platformer but unfortunately the sliders all wouldn't be close enough to fall through the bomber hole at the very end. Hence, that's why I needed to use the shimmier to get the builder to sync up with the rest. Otherwise, the solution is very hard to see. In particular, finding the correct RR to make everyone stack behind one another took a really long time. I apparently don't understand the RR mechanics too well

Aquarius 3 -
Jumping Bees Not as hard as the previous two but I still struggled a lot. That was a very nice trick of platforming and blocking at the end of it in the starting area to allow a lemming to go over the top to prepare the right side. Here, I have a jumper leftover, but that's because I timed it in such a way so that only one lemming slips by the platformer while he's in progress and he closes off the gap in time before anyone else can slip by. Therefore, it's really to make the timing much easier by simply having one from the crowd jump over the blocker. Also, that's a very nice trick with bombing a faller in order to get the swimmer to jump into the pool, as well as bombing the top to get him out. Finally, jumping and bombing to make a hole that everyone can get into after the platformer is done in order to make a safe drop down close to the exit. Overall, quite a nice level here!

I honestly don't know why I struggled so much with this level after solving it and seeing that it's not very hard

In particular, I kept thinking that the platformer bridge needed to be bombed or destroyed with a skill to isolate the swimmer when it was really simply getting one to slip by. As you already mentioned, my solution isn't intended, but it is acceptable. From what I remember, you said that the intention was to send a worker out to the left.
Aquarius 4 -
Rhythmical Another hard one but unfortunately my solution was a backroute. I really love what you did with the design there by putting in a lot of musical symbols: two eighth notes joined I think it's called a stem, an eighth note with a flag, a treble clef and a bass clef. I've been interested in music for a very long time, as even before I took choir in school as an elective I've been singing a lot and hence I know a lot of music theory

Aquarius 5 -
Abandoned Library This is a level where the solution is obvious, so the challenge is getting it to work. Even then, it's still a challenging level. It was extremely annoying that the solution I tried for the left entrance always failed by a pixel or two, as well as being a builder short

This is the builder I would have had had it not been for the fact that I needed a builder to keep a miner going where the lemming is trapped in the middle

In the end, I found a hackish way to release the right crowd with, which there are now fire traps to prevent. However, with the addition of a button, I think it's clear that you intended a falling bomber to release the blocker.
Aquarius 6 -
RefleXion Very hard level, and one that you guess is a roadblock. Indeed, I agree with you here, as I really struggled here. In the end, I found a solution that simply involved holding the crowd back, which you decided to block off by putting in a time limit and adding some terrain so that the blocker can't be released as easily with a laserer

So, it seems that the intention is to keep the crowd moving, although I honestly have no idea how to solve the level now

This isn't the only one, though. There's plenty of others that I don't really have a clue anymore.
Aquarius 7 -
Double-Edged Sword Somewhat an easy one for the rank, although it's pretty much the only level that I considered quite close to a breather for rank 5. I have two bashers leftover, because apparently turning a lemming around with a walker as soon as he touches the ground after breaking through is enough of a lead for him to build over the gap at the bottom. Again, my level was considered a backroute, so apparently you're not taking this solution for an answer

Aquarius 8 -
Purity and Industry Another very deceivingly hard level. In the end, I found a solution that involves a lot of precision, especially with the platformers both going at the same time so that no one gets interrupted and turns around. It also uses the extending the very first basher at the very first start with the builder staircase going in the same direction as the basher, but it's a very precise skill assignment, as you need to do it at a time so that the basher doesn't stop but at the same time the builder doesn't overtake him and hence gets contained by the tunnel. With the backroute fix, seems that the trick isn't the intention. My guess is that the intended solution somehow has the glider go through both the middle and bottom of the level, but so far all my attempts is always running a skill short. This level definitely reminds me of "The Gaema Plateau" due to how if you take the obvious you'll always be a skill short. Seems to be working here very well!

Aquarius 9 -
IRON JUGGERNAUT 2 Wow, this is a really good level and one of my favorites!

You really did justice with Icho's level from United here. This one still ended up being a difficult one for me, although it wasn't anywhere near as hard as the original, at least for me due to how there's no stackers here, and I tend to be very bad with them. I do like the solution concept, involving both a climber and a slider working their way through various parts of the level to have the path set up. The slider/shimmier goes through the bottom, while the climber that frees the slider so that he doesn't go out in the wrong direction goes back up to the middle of the level after the OWW is bashed through. However, you have deemed my solution to be a slight backroute due to how one of my miner and blocker placements are unintended, I believe.
Aquarius 10 -
Triple Lutz This one doesn't seem as hard as some of the previous ones in the rank, but it's still challenging. Now that you blocked off my solution with a lot of fire traps, I'm not sure how to go about solving the patched up version either

Aquarius 11 -
Lost in an Ice Cave Backroute here as well, as I'm certain the solution is supposed to be far harder than that. Whereas an easier version of "Polaris Rhapsody" was in the Aries rank, this is the level you stated is pretty much a far harder version of "Polaris Rhapsody." Therefore, that likely means the solution involves getting a blocker in place to bounce off a miner, as those two levels both involve such a thing. Not sure how to go about doing that with the fix

Aquarius 12 -
Butterfly Effect Another level that you guessed would be a roadblock, which I also believe. Hence, my solution is a very bad backroute. With the patch, once again I don't have the slightest clue to go about it.
Aquarius 13 -
System Malfunction Another very bad backroute and a level which you also guessed would be a roadblock. Not sure how to go about solving this patched up version either

Aquarius 14 -
BlockChain Company Revisited A repeat of Aries 8 but far harder due to having 5 less of every skill. In other words, both are X-of-everything but with the challenge much higher with the repeat version due to the buttons. You already mentioned that my solution is more efficient than yours, where I had some skills leftover but you used all the digging destructive skills. Pretty much an anything goes level just like the original, hence we finally get to a level that doesn't need a fix after I have backrouted every single one of the previous 10 levels

Aquarius 15 -
Simulation: FARO Yet another one that you listed as a roadblock, and I certainly believe that after a lot of struggling here despite finding a very hackish and super bad backroute

Indeed, that solution has now been patched out by switching around the pickups. So, once again no clue how to go about solving the patched up version

Aquarius 16 -
Facade of Indifference Another level you listed as a roadblock, and I can definitely see how, but honestly this one isn't so bad, now that I think about it. I was simply a dummy with the right side, where I never though about using compression to get past the masher trap in order to save a skill that is useful elsewhere

This level is interesting, as this was patched up before I managed to solve it on camera. Thus, you'll see two different versions in the LP, an unpatched version and the current v3.6 one. The changes on the left side definitely made the solution more obvious

Even then, this is quite a nice one, although admittedly it's annoying with how the shimmier has to be repeatedly assigned with the rough terrain in the middle with the slider. No fault of yours, though, as that's just how the skills work.
Aquarius 17 -
Forgive Us Third level in a row that you guessed to be a roadblock, and yes I believe that. Once more, the problems usually lie in being a skill short. I'm not sure if being able to glide onto the mass of terrain is intended, but that's how it allowed me to have enough skills to solve the level. It even allowed me to have a shimmier and jumper leftover

So, perhaps another backroute?
Aquarius 18 -
One Lemming to Rule Them All The final level you guessed to be a roadblock, and indeed it was very so here, as I really struggled here. This was another level that needed off-camera time to solve. In the end, my solution is probably a backroute, as I have a blocker leftover. For some reason, it took me a really long time to see to use a jumper to interrupt the digger after he's gone low enough to stop any of the crowd from spilling out to the right. Also, as this is one of your favorites, you mentioned that they usually don't have anything fancy or advanced required, so I'll keep that in mind. Indeed, there wasn't really any of that, so it's likely I struggled due to really overthinking and overcomplicating the solution.
Aquarius 19 -
Immoral Society I believe this is only the second level of the pack to have at least one neutral. He turns out to be very important in the solution, as he needs to disarm the traps and swim over to get the final button right where the exit is. This wasn't guessed to be a roadblock, but I thought this level was still hard. I'm not sure if getting those compressed lemmings past the traps is intended. I also used the odd shimmier can still go through a platformer bridge mechanic to save the lemming who platformed over the water to allow the right entrance to land down safely, as I wouldn't save enough otherwise. I also don't know if it's intended to punch a hole in the stack to allow everyone to be contained on the right side, as well as the super precise stacker placement to allow the neutral to turn around to get the top button. I also constantly kept forgetting the neutral is a preassigned climber, swimmer, and disarmer all in one

As for the zombie, he simply seems to be a "keep away at all costs" and therefore there is absolutely no need to come anywhere near him.
Aquarius 20 -
Lovebirds Duet To round off the pack, we have a wonderfully designed level by Armani's gf. I especially love all the hearts everywhere in the level, signifying their love for one another

She did quite good with the design. In the end, this seems like a very bad backroute

I still like some solution parts in my earlier attempts, particularly the builder/miner combo, so I honestly don't mind my solution being blocked here, as it deserves to be quite special due to your gf making it and you coming up with the solution via the skillset. It's just that there's still the problem of skill shortages again

All in all, still a very hard level, although certainly nowhere near the hardest of the entire pack like with most level packs I've played and completely solved.