Pickaxe 1 -
Zigzag World Nice level to start off the rank, although I think this might be a bit hard for its position despite the open-ended nature of the level. Then again, there isn't any complicated synergies with the miner skill required in this level, unlike some of the next few which do increase the difficulty a bit.
Pickaxe 2 -
Thunderclap Ah, another Patience/From the Boundary Line remake. Seen too many of these, though it's amazing how so many solution variations to this level exist! Perhaps it's just an iconic level in so many ways, being the second level from OL to feature a 99RR, for example. Similar to the previous level in that zigzagging miner tunnels are needed to get the crowd down safely without splatting. Solution won't work with a 99RR, though with a blocker it will be possible. I also like that you don't mind low enough to release the crowd but you later build to release them. Somewhat obscure but it can be very useful to keep in mind!
Pickaxe 3 -
Out of Salt Ok, I was a very big dummy here in that I kept thinking to use the builder to stop miners going to the left when I kept overlooking the whole use a builder at the top of the steel to stop climbers going out to their doom. It's actually much simpler than that, though here one must use miner tunnels in progress to turn around climbers so that you once again alternate miner tunnels in both directions until you get low enough to mine the crowd out. I can still see this one catching less experienced players off guard.
Pickaxe 4 -
The Escape Artists Once again, I was a big dummy here for a while in that I kept doing the miner in the wrong spot so that I can release the blocker with a digger shortly after using it to turn the miner but then the miner won't stop because he's too low. I definitely owe this to the huge lapse of time since I last played the pack on Lemmini and hence I can't quite recall all the solutions detail for detail. Of course, doesn't matter as I can still figure these out again on my own.
Pickaxe 5 -
Triumph For Their Magic Picks I believe this is the first custom level where I learned the whole miner can cancel out another miner on Lemmini. Nice level but can otherwise be frustrating to pull off since it requires very good timing. Also I believe the solution works out a little differently due to how you can backwards mine on Lemmini to stop climbers going out to their doom, but that was eliminated from NL, which therefore makes it a bit harder to stop them from getting into danger. However, I don't use the other climbers anyway, so doesn't matter. In addition, lemmings on Lemmini still go out in the same direction rather than turning around when hitting steel, so one could use the hitting steel to turn on NL, though one still needs to stop him from going out to the left in the area to the right. Nice red herring exits!
Pickaxe 6 -
Evil Sandglass Almost a complete breather, though the thing that took me a while was to stop the non-climber from the bottom left entrance from getting into danger. I overlooked the bashing and then building to stop for a time. Otherwise, I like how you have to beat the top lemming and save him with a splatform while he takes an extremely long detour with multiple twists and turns in the little maze.
Pickaxe 7 -
Have Skills, Will Travel Ah, I remember this one and it's one of my favorites of the rank!

Again, miners won't turn on steel on Lemmini, but the solution is still more or less the same as here, just need to delay them on the second builder staircase. I remember the satisfying feeling of first figuring out that stall tactic with the miner/builder staircase. I do recall this coming in handy with some levels from ssam1221 for Dos/Lemmix.
Pickaxe 8 -
Miner Under Control Simple one, though it's a bit hard to see that the worker who builds to the exit must turn around to bash at the bottom rather than make the miner do the bashing, as you'll actually run out of time if you do the latter! Hence why you're allowed to lose 3 rather than 2. Thus a case of an absolutely necessary timer, almost similar to my R2 of the previous LDC.
Pickaxe 9 -
Hugs & Kisses Solution is obvious, but getting the execution down is extremely frustrating, as the two miners must cross each other without either one cancelling successfully. Fortunately, this is the only thing required in the level.
Pickaxe 10 -
At Least I can Count to 10 I remember this one stumping me for a while, especially with the very tight time limit. Also the solution isn't easy to figure out. In particular, the little ledge to land on on the very far right is quite sneaky. I remember all of a sudden discovering it when I just let a lemming drop and saw that there's a brief moment when the lemming is walking more to the right.
Pickaxe 11 -
Descent into Hell Another one where I was a big dummy, where I kept thinking to have the miner and digger go at about the same time, when in fact you're supposed to block almost before the miner breaks through the left side and then dig all the blockers free except for the one on the far right. Quite a nice level here when I got the solution down!

Pickaxe 12 -
Bricky Madness Another iconic level where the central Lemmini mechanic here doesn't work (blocking on one side of a tiny gap so that the climber will hoist and turn around and reach the platform on the other side). Because of this, the hardest part here was figuring out how to get the climber to go out to the left side to get the bottom crowd to the left exit. Here, I actually don't use the blocker pickup, though I don't think this is a backroute, as it's simply to avoid any timing whatsoever. Still a nice level and adaptation to make the solution work! Nice job, Icho

Pickaxe 13 -
The Drowning Walk All about getting everyone to turn back to the left except for one. Easier said than done. I have to suspect it's actually possible to save everyone here by successfully getting both miners going in opposite directions to cancel out, like I did with one of your War levels from United, but I couldn't bother myself to get this to work, as this is extremely difficult to pull off and just not worth the time and effort. Should also be possible on Lemmini as well, though the miner is very wonky and weird due to floating in the air for a brief second or so after taking a swinging stroke.
Pickaxe 14 -
A Neat Climb-Down Another iconic level on Lemmini, where I do believe it involved a climber infinitely climbing a miner tunnel in progress. No such thing here for NL, therefore the solution is completely different. Took me a while to figure out how to get everyone down safely. I kept thinking to get into the middle pillar to drop down past the exit to build to make the path for the floater down the far right side, but this turns out to be completely wrong. Nice, decent level even with the solution adaptation!

Pickaxe 15 -
Unwilling Funambulist Nothing too hard here either than you need to rescue the hatch quickly before you lose too many. I definitely remember this one.
Pickaxe 16 -
The Oblique Conundrum Solution can be somewhat difficult to pull off, though it's necessary to get 2 to go on ahead, one to climber bomb the pillar, the other to mine and then build to the exit, without the second one turning around before bombing through. I think one will run out of time otherwise. Nice level though!
Pickaxe 17 -
Fish Fry Ah, I had a lot of the solution down and then missed the hole to turn around the worker lemming in on the bottom left. Originally required the odd miner mechanic on Lemmini where you can cancel one by assigning it a blocker due to how it's hovering in the air on that engine. However, the closest you can simulate that on NL is by cancelling with the walker skill instead. I wonder if the solution can still work without them by providing 1 more builder skill just so only the original 8 classic skills are used rather than a NL exclusive skill, though if I'm not mistaken isn't this skill also found in Lemmings 3? I've never played the game, so I don't know.
Pickaxe 18 -
Lemmings on the Road to Ruin Another iconic level where a digger and miner must cross without either one cancelling successfully. Pretty much the level that I discovered it's possible, similar to the earlier level of two miners crossing each other without cancelling in the rank where I first discovered this. Here, I got to say it was super frustrating, as I kept needing to readjust the positions of the miner and digger until neither one stopped. I like the solution overall, just the one part with the miner and digger not working when you want it to can be frustrating.
Pickaxe 19 -
Topsy-Turvy Another iconic Lemmini level that relied on the solid level sides which behaved very peculiarly. However, as level sides are deadly in versions of NL after very old formats, the level needed some adaptations. Of course, one could just use one-way force fields to simulate the Lemmini behavior, but I think it would require grabbing it from another tileset, as the Marble one doesn't have them. It's also harder to pull off on Lemmini, as it can be hard to assign the builders right on top of the other to make an impassable wall to prevent the others from walking and dropping to their doom.
Pickaxe 20 -
Eye of Rambaldi Another level where you need to get two miners to cross each other without either one cancelling successfully, though it goes a bit further than that in that you also need to turn the miner with a blocker and use builder staircases to extend the miners. Here, I was stupid in that I kept thinking to assign the blockers at a much later time, but what kept happening was that the miners would turn and one of them kept making a hole in the floor and the others would drop to their doom to the bottomless pit while the other one is successful in getting the others to the exit. Instead, the answer is to use the last one to block while everyone is still past the blocker long before the miner reaches them to turn. Even then, it can be super frustrating to get the miner placements correctly on either engine. Nevertheless a nice level to finish off the rank!