An updated experimental version is attached here and to the first post. Changes:
- No OhNo-animation for exploding shimmiers (and reachers)
- Raymanni's improved shimmier sprites
- Pickup-sprites for all graphic sets.
Graphic set creators are encouraged to look at my suggestions and modify them, so that they are happy with it. At the very least, please check, that I haven't forgotten to update your style.

Do we have sprites for Christmas lemmings yet?

No. Good point. This is another item on my ToDo-list. If anyone wants to step up an adapt the christmas sprites, they are very welcome to it.

But so far, I can't use them yet because I still get an error that the lemming animation metadata for the Reacher can't be found (and I guess for the Shimmier as well; Reacher just comes first in the alphabet, hence it's probably just the first error message).

Assuming you have just recolored them, not changed their size, moved some sprites, ..., the fix is pretty simple: Copy the file "scheme.nxmi" from "styles/default/lemmings" to your folder with the curstom lemmings sprites. This file contains some meta information about all the lemming animations, e.g. where the image should be placed relative to the in-game physics position of the lemming. At the moment the game wants to read these information for the reacher and shimmier from the file, but doesn't find it, returning the error message you see on your screen.

Seriously, what a great Christmas present to the community! I was kind of secretly hoping for this to happen, but didn't really dare to... I hope you didn't work over the holidays to get this ready, but had it finished a couple days early and just waited for the appropriate time to release it?

If I had it ready before Christmas, I would have released it then. But during the past week, I had more free time than in the whole past month, and I put it to good use.

Okay, just a question: In my thread about anticipated Shimmier behaviour, Nepster said the plan was for Shimmiers turned into a bomber or stoner to explode instantly (=at the ceiling). Currently, they turn into ohnoers and fall down.

Thanks for mentioning this. The OhNoing is not intended and I still feel that instant explosions would be more consistent.

I intentionally omitted a description of the exact mechanics, because I wanted people to focus on how the shimmier feels, rather than whether it is consistent. Still, thanks for compiling the list.

6.) Shimmiers will stop if the ground gets too close to their feet. I don't have the exact threshold here as in clear physics mode I think you can't currently see the exact position pixel of the shimmier. Can you give the exact ammount here, Nepster?   (Bottom left chamber)

Depending on the shimmier frame, the lemming sprite is 8 or 9 pixels high. The phyisics position of the lemming is 9 pixels below the ceiling, i.e. is one below the feet if the sprite is 8 pixels high, and at feet level if the sprite is 9 pixels high. A shimmier will transition to a walker, if the space between ceiling and ground is at most 9 pixels, i.e. if between (and including) the physics lemming position and the ceiling there is at least one solid pixel. In particular this meanse, that the basher tunnel with its 10 pixels height is the smallest tunnel a shimmier can traverse.
Regarding not being able to see the shimmier position: This seems to be a general bug, that I noticed as well: If the first level you start is one without a hatch (without having started any other level before!), then the lemming position will never be diplayed (not for shimmiers, not for walkers and nor for any other lemming). No idea, what causes this and what the exact conditions are to reproduce this bug.

WARNING: This is still an experimental version and any of the shimmier physics may still change! Do not complain if they break the levels, you create with this version.

After the usual warning, here is the good news: This experimental version allows you to test the shimmiers. It should not crash every ten seconds and shimmiers might even somewhat behave like you would expect them to.

Installation:
Although the stable version should have no problems with the modified graphics for the shimmiers, I still recommend starting with a new installation of the stable NeoLemmix version (or a copy of your current one). Then extract the attached zip file in the folder, replacing the older files with the ones in the zip file.

How can I create levels with shimmiers?
The zip file also contains a new version of the editor, that supports shimmiers. Alternatively open the nxlv file and add among the other skills a line like "SHIMMIER 20".

What should I look for in this experimental version?
1) Crashes: I might have overlooked some places, that have to be adapted to the existance of a new skill.
2) And equally important: Anything that didn't feel right or suprised you. I would like the shimmiers to be as intuitive as possible, and we are now in the unique situation, that there are a lot of players with a fresh mind and without preconditioning by previous shimmier versions. So please report anything that caused a raised eyebrow.
3) Whether the animation looks good. For the shimmier itself I used Raymanni's sprites, so I am less worried there. But the reacher animation might very well be something that can (and should?) be improved upon. As I mentioned frequently, I am not really good at creating sprites, so if you can improve the sprites yourself and post the new ones here, it would be much appreciated. (But even comments like "Frame 5 of the reacher animation looks out of place" do help).

What is left on the ToDo-list?
- Hunting for glitches (though this will have to wait until the main physics rules have stabilized)
- Adapt the pickup-skill sprites for non-default graphic sets. Currently you can only use shimmier pickups, if the graphic set uses the default pickup sprites.
- Add support for shimmier talismans. The player should already be able to handle them correctly (though I haven't tested it yet), but the pack toolkit doesn't allow creating such talismans. 
- Fix all the issues you will find.

Thanks for the bug report, but this feels like a low-priority and high-effort bug to me. So for the moment, this goes on the stack of stuff to do, whenever I have nothing more productive to do and need a challange.

Done

Sorry, but this is not nearly enough information you are giving us here. My current guess is that either the level pack of this level overrides the default messages, or the file with your default messages got changed, so that the top message got replaced with the one you are seeing. The messages are stored in the file "data\postview.nxmi" and this file should look like the attached one.