I've started a playthrough of this, and just like with GigaLems, I'm recording videos as I go.

https://www.youtube.com/playlist?list=PLVWvcY0oGEFwuPbo0EkolrRUn-OLNfHUQ

Already noticed and watched it

1.) Download Link:

NeoLemmix player: https://www.neolemmix.com/

Lemmings Reunion (V 5.2  ~ 308 KB): Lemmings Reunion V 5.2
Contains the level pack in the newest version!

Lemmings Reunion Music (~ 80,6 MB) : Lemmings Reunion Music
Contains the music tracks! Extract all the tracks into the "music" folder of your NeoLemmix player. If the player does not have a "music" folder yet, create one in the same folder where the player is located.

Outdated Old formats version (before NeoLemmix 12.0.1):
Lemmings Reunion (V 3.3  ~ 293 KB): Lemmings Reunion V 3.3
Contains the level pack in the newest old formats version! Uses the same music pack.

To update you only need to redownload + replace the files of the previous version. The music only needs to be downloaded + configurated on your first download!

2.) Installation:

1. Get a NeoLemmix player from: https://www.neolemmix.com/  and extract it into a folder of your choice (if you already have an up-to-date player you can skip this step)
    Also make sure you got all the styles that are linked in the player section there as well and extract them into your player's "styles" folder. The pack uses some non-standard tilesets and
    therefore needs the collection.
2. Unzip "Lemmings_Reunion.zip" into the main folder of your Neolemmix player.  ../levels/Lemmings_Reunion should exist now.
3. Extract all the music files from "Reunion music.zip" into the "music" folder of your NeoLemmix player. If the player does not have a "music" folder yet, create one in the same folder where the player is located.
4. Run "NeoLemmix.exe" and press F2 in the main menu so you can access the pack through the level browser.
5. Inform yourself about the basics, new NeoLemmix features and hotkeys with the manual: https://www.lemmingsforums.net/index.php?topic=4081.0
6. Enjoy!

3.) Ratings:

I'm too young to die

No Knight Shall Die!:

In the first rating you will encounter tutorial levels, a few go to the exit ones, levels teaching you basic tricks and your first real puzzles. Don't expect it to go as slowly as the original game! (The final level of the rank will prob be a spike as it counts on you using a bunch of tricks you learned so far)
(Fun-Tricky)

Hey, not too rough

Rock and Metal:

Puzzles are getting harder, the tricks you learn will be advanced ones and even some pixel-precision will be needed.
(Tricky-Taxing)

Hurt me plenty

Whispers and Lights:

It gets a lot harder here. Levels getting way more difficult and longer and you have to frequently use all the tricks you learned so far. Sometimes think outside the box!
(Taxing-Mayhem)

Ultra-Violence

A.M.:

Now it's on! It is getting frustraiting sometimes and you have to use everything you got.
(Mayhem-Beyond)

Nightmare!

Justice for Heroes !:

Are you serious? Let's find out! The first ~ 15-18 levels will be just plain hard, but then . I am no longer your friend here! I am your worst nightmare! Levels are mostly long, complex, require perfect precision and everything out of your trickbox. They will be frustraiting, but consider: THIS IS THE NIGHTMARE! RATING and not the cuddle one!
()

4.) Thanks to:

namida                           for helping me along the way and with all the programs it took to convert the pack onto NeoLemmix
Plom and GigaLem         for making the mainmenu logo and the rank signs for me
Nepster                          for testing the Lemmini version
Akseli                             also for testing the Lemmini version
Vurez                             for three of the music tracks (Medival Arrengement, Tetris and Memories of the Green-Haired folk)
                                      Youtube: https://www.youtube.com/channel/UCy6yLi_53JfvJxSwNtdalWA
DJ Alundra                     for one of the music tracks (Medival remix)
                                     Youtube: https://www.youtube.com/user/pussi24/videos
Arachnosoft                   for one of the music tracks (Lemmings medley)
                                     Youtube: https://www.youtube.com/user/arachnosoft/videos
Numac                           for the rank finisher tracks
                                     Youtube: https://www.youtube.com/user/NUMaCmusic

5.) CONTACT INFO:

Via email you can reach me at: ScavengerW@gmx.de

Youtube: https://www.youtube.com/channel/UC4Elfo3E1jTl-SHlOy97kwA

Now have some fun with Lemmings Reunion and send me a few replays to get the last pesky backroutes!

If you have 150 levels, I'd assume you wouldn't have more than 150 musics at most? The toolkit should support up to 252 tracks... if it's not letting you put in this many, it sounds like a bug. PM or post here exactly what happens, whether htere's a consistent point, etc.

I thought it is still in the making, then it will be fine. I give the levels the track numbers in the editor and create the actual music list in the Toolkit.

Only 40 levels left to convert!

Music is also nearly ready and already converted (90MB overall   ~ 40 tracks) and got the first positive answer from one of the three guys who created some of the musics tracks:laugh:. The rest is "free to use" .
The music of all three creators already have a free download link underneath them, but I felt that at least I shloud inform them that their music might be in a game if they give the OK (apart from that most of the tracks were already lemmings related and they might be very happy to know about this:)).

Who these creators (and their awesome music) are will be revealed in the actual release post. This will be my little secret for now!

Side note: I noticed that the autosteel function does not properly work with converted custom Lemmini tilesets (was not a deal at all though, as I used my old steel areas). I guess the steel pieces are not properly labeled as steel, but I think that would be nearly impossible to fix (I just want to inform ).

Version 1.5 is out! It focuses on fixing the difficulty curve:

2 01 <-> 2 12
2 03 <-> 2 09
2 07 <-> 2 15
2 08 <-> 2 24
2 19 <-> 2 23
2 10 <-> 2 21 + giving the new 2 10 additional Lemmings
2 20 <-> 3 17 + giving the new 2 20 an additional min so even less optimal solutions will work
3 13 <-> 3 06
3 07 <-> 3 27
2 28 -> 3 21 -> 4 06 -> 3 04 -> 3 01 -> 2 28

With the now fixed curve I will continue with converting the pack.

If there will be future updates, they will be based on if you send me more replays with backroutes in it (mostly backroutes of the already "fixed" ones or the not yet beaten 5 29 +5 30).

Problem solved. Made a mistake everything is in order .

Another problem has appeared. Or an old one actually just with another custom set: The conversion of the Egyptian L2 Lemmini style to NeoLemmix still creates (as with Castle before the fix) black holes within blocks. (Shame on me to forgot to put one of these style in the test program.........it could have been delt with at the same time )
As you described the castle problem, it may be just as easy to fix this as the other problem.