Looking at my levels nowadays, lots of them require maybe excessive release rate tweaking, that might create unnecessary-ish artificial difficulty. When creating these levels, I thought I wanted to hide the solutions pretty well with those RR tweaks, so that no solution would be encountered by accident. But as said, release rate regulation makes the levels harder in lots of these cases, maybe harder than needed in the end.

Sparkle & Glitter I saw in a dream when I was a child and it's surprising to see how well it kind of works as a level, having few little tricks in a very minimalistic landscape. Early backroutes happened due to time limit being too lenient for unwanted approaches.

The Glade of Disbelief is built around that trick, about which Simon/IchoTolot even drew a concept art of how the builder check works.

For Mr. Dodochacalo and Mr. Pieuw is the only level I didn't try to hide the solution at all and alongside Crysilis and Zygoptera these levels that are still the only ones that aren't backrouted in any version of the pack. After all, it is a tribute level.

I didn't know that Winter Solstice is in Revenge of the Lemmings or even has a NeoLemmix version. Obviously, the miner shouldn't work on the left hatch area what it does in the NeoLemmix version now when watching kaywhyn's solution from YouTube. Also, this level has a visual quirk: the water pool on the right was designed to have 4 layers of ice on the surface, but it seems than only played in Lemmix those appear as intended (the lowest object is on the front and the highest on the background). In these other versions there's those mud layers instead of ice surfaces, it doesn't look as nice as I mentioned it to be. I guess it's possible to be fixed, though.

Feel the Pressure is the first level I ever released, it was in a Lemming level contest with a rule to design an 1-of-everything level. It revolved around the idea of merging Lemmings from two hatches in a digger pit with a RR of 87. Again, I don't think I have taken much part of the Lix/Lemmini/NeoLemmix versions of this level, but the save 47 solutions I've seen are ok for me.

Why do you all look the same? had earlier title "Why do you all look so similar?" if someone wonders if there's replays going around with that name, for example. The main trick is the main thing here, but as said, release rate fiddling makes things a bit hard.

In the Core is the only level with a clear glitch but as mentioned in my starter post of the topic it can be quite obvious to find out in the end. My solution actually involves releasing both crowds from below, I didn't even remember this before looking at my old replay. IchoTolot's solution is similar to kaywhyn's.

IchoTolot found a ridiculous backroute solution for Pedantic Lemmings in 2015 and I haven't bothered to fix it... others have found that intended solution of re-using the climber. I made the pack with all of 9 original tilesets from the games (excluding Xmas), and I chose my favourite tileset, Brick, to be the one used in two levels.

Crysilis was made in a level designing jam with a rule of making a builderless level. The title refers to the Crysilis planet level in Jazz Jackrabbit game. This is the most open-ended level in my pack and is pretty much any solution is fine type level. Yes, the right hatch area is pretty much filling compared to the two hatches area.

I can't remember exactly if Zygoptera was first a visual idea before deciding the main solution there, most probably it was. A fun fact: I wanted to use the cooler sounding name Zygoptera (damselflies) instead of Anisoptera (true dragonflies), even though the visual appearance of the level is maybe closer to Anisoptera. Also as I studied biology in the university it was nice to have something related to that in my level pack. In the solution my bomber and digger assignments are vice versa to kaywhyn's in their YouTube video and it's completely fine. Crysilis and Zygoptera are the two levels I initially meant in my original post saying "I'm a bit worried if two certain levels resemble each other too much." referring to the usage of basher mechanics.

Mutilation 10: Twisted Track -  This is somehow a hard level for me. A digger and a blocker saved, so not intended I guess?
Mutilation 14: Started From The Bottom... - Similar than my previous solution, but now I needed to use the bomber.
Decimation 2: The Winning Edge - This feels intended. The structures on the right did matter after all!
Decimation 10: Across The Sky - Okay, now I had to juggle with three of the cloners. One bomber and thus an extra guy saved.
Decimation 12: A Lot Of Lemming Going On Here - My solution barely works, basher+platformer+builder placement is pixel precise in its height, and the time limit is just enough with this crowd cycle. An extra lemming saved.
Obliteration 3: Lemming On A Prayer - Okay, this I had spoiled myself because I solved it already via backroute and then read the hint. :p

Obliteration 4: White Noise - I am not even close on this one yet. I thought my best attempt was crossing the digger and basher but I don't have the means to turn the worker lemming around at the right side of the level to build a bridge over the water for the crowd.
Obliteration 9: Aquadynamics - Skipped at first and solved after Obliteration 10-12, when I realized that I could actually take both lemmings over the one-way wall at the right.
Obliteration 10: Dirty Joke - The one-way stacker was the key element in the middle of the level.
Obliteration 11: Bending the Rules - This is most probably a backroute.
Obliteration 12: The Golden Rule of Lem - A ferocious looking level, but really fun to play! It's always a good feeling when one plays a level that seems huge but it turns out to be a lot more accessible than one would think at first.

Decimation 11: Caving Under Pressure -  My approach is brute-forceish so I really think there's another route which is intended. I didn't work on my way with the crowd control yet before finding the correct digger-builder placement for the blocker release in that mound (I tried it from the both sides of the blocker, both the worker lemming and a crowd lemming, both digger facing at the blocker or away from blocker).
Decimation 15: The Longest Minute - This is a failure by one frame, that one guy eagerly goes to the void. I'd think that my skill placements are correct. I also did this level so that the last entering lemming was already hopping to the exit but the timer went to zero.
Obliteration 1: A Severe Case of Lemmingitis - A breather here, a really straightforward level.
Obliteration 2: Good Lemmings Die Young - A good and well-placed level.
Obliteration 3: Lemming On A Prayer - This one I suspect backrouting.

Mutilation 4: Jump Scene - Basher saved. Also this is clearly the easiest level in the pack.
Mutilation 14: Started From The Bottom - Climber and bomber saved.

Decimation 3: Lemming Semantics - A nice map, solved immediately though, so should be in the first half of Mutilation probably.
Decimation 4: Oh Blast... - Same here, though again this nice trick of yours from Dead is the New Black and Odyssey.

Decimation levels 1, 3, 4 and 6 are solved as fast as Mutilation levels, so there's no apparent difficulty gap there in my opinion. Mutilation has a nice difficulty curve, though especially levels 13 and 15 are harder than this first half of Decimation, probably on purpose.

Decimation 8: Mission: Difficult - The good old stepover turnaround saved me after trying the super annoying pixel precise fatal fall for non-glider climber, grr!
Decimation 10: Across The Sky - I didn't use cloners (for other than reaching the save requirement).
Decimation 12: A Lot Of Lemming Going On Here - Floater and extra lemming saved.

My solutions for both Decimation 11: Caving Under Pressure and Decimation 15: The Longest Minute fail by single pixel or frame, even in different attempts, so I'm now quite worn out by these two...