Merged from Jumper & Climber turn & continue when encountering a wall/edge of level - this is because the discussion has ended up covering quite a range of topics, but can be mostly summed up as a discussion regarding level sides physics.
Wow, quite a lot to respond to here, I'll try to be concise in my responses, if not brief!
TL;DR version here.
Well, there go my hopes of ever converting Lemmings Open Air to Super Lemmix
On the contrary, it's an opportunity to make
a brand new port of that pack, which makes use of SuperLemmix's new features. I'll be converting my own packs (not all of them, but the main ones for sure) and will likely make small tweaks or even huge overhauls to many levels.
If you don't like the idea of having to go through all of that, I'm sure a few people wouldn't mind doing some of the work for you

With that said, this topic is asking if we
should go ahead with this change, not stating that we
are. I'm still somewhat convinced that this is the way to go, but perhaps less so after reading some of the comments.
I always wanted to be able to turn them around
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I haven't really gotten into using Super Lemmix all that much yet.
Which is a shame, because I really want to like it. Especially because it has a bunch of features my earlier self, in the first few years I was on this forum, would always have wanted:
Pretty much SuperLemmix's raison d'etre; it does the stuff it's better-behaved sibling doesn't want to do!
EDIT - I jest here, because I actually would like SLX to be equally well-behaved, just in different ways.Seriously though, we have an opportunity here to reopen discussions and reconsider some of the possible differences that could make it a full-fledged alternative engine. I personally think that's quite an exciting prospect, but then - as dev - I would!
The packs you've made for NeoLemmix will always be available for NeoLemmix - and, as others have said, I think the two will end up coexisting as alternatives. This gives you an opportunity to either remix your existing content to fit SuperLemmix or, better still, make some new content that leans into the platform-specific features.
set apart Super Lemmix even more from NeoLemmix, so that both engines can serve more and more different purposes, therefore feel less redundant to each other, and maybe encourage more and more players to use both engines in parallel.
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iHowever, the cost of this reduced overlap will also be less common content for NeoLemmix and Super Lemmix
To the first part of this - yes, exactly! This is ideally what we want. Opportunities to make content for both engines is a good thing.
To the second part - my instinct here is that packs ought to be released for one engine or the other, rather than both. Then, we accept that there will be some cross-compatibility issues with
some (but probably not all) levels; I think this is a small price to pay for the possibilities currently on the table. Or, of course, make ports for each engine if time/inclination allows. There are already several packs available for multiple engines, and it isn't really that much work to make it happen, from experience.
Then again, most of my packs are less than 100 levels long - I can imagine a pack as large in scope as one of yours or Flopsy's would be much more difficult to manage for both engines. For that, I would again honestly suggest that you ask someone from the "SuperLemmix community" (should one emerge) to help you out with the port.
I just found out you made a converter tool, specifically for the purpose of converting NeoLemmix packs to Super Lemmix. 
Did I? That's news to me! It has its own Editor (which is also based on the NeoLemmix one, but makes several of its own divergences and will likely continue with that trend), but I'm not sure that's what you mean!
I don't really regard the Freezer as a "new" skill, merely a "different" one - just like the Cuber in Lix
Except that it can now be rescued!

I don't agree [replying to the OP], because the shimmier is not like the other skills you mention. The swimmer is a permanent skill. When the swimmer hits a wall, it turns around (obviously) and is still a swimmer, so it swims the other way
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The shimmier is a single-action skill ... It just makes sense that hitting a wall is something that makes it stop
Yes, good point. This certainly counters the first of the main arguments in favour of turning & continuing.
How about this as a possibility - instead of falling straightaway, the lemming turns and transitions to Dangler. This would then give the player the opportunity to assign another Shimmier, should the need be to keep the lemming Shimmying rather than letting them fall... better, perhaps? I like it less, since it costs more skills, but it feels better than them just falling straightaway with no opportunity to perform another action.
And, to be clear, I still mostly prefer turn & continue despite the given counter-argument, which is certainly compelling. Any more thoughts on this?
For me, the main reason against bouncing is that it allows for some really fiddly design, particularly bouncing off a wall to reach a ledge above
As long as the designer doesn't make it so that the action is only possible on a single frame (maybe this will form part of "SuperLemmix philosophy" -
if it can't be done in real-time, it's bad design), I can't personally see this being an issue. Even
Save Me allows 2 frames for its infamously pixel-perfect ending. I'd say 3 frames is about right for this sort of thing, 2 is a bit mean but still OK, 1 is bad design.
Also, we have the opportunity to do something different here than what was decided for NeoLemmix. There would be little point in following through on the conclusion of old discussions unless the majority of us happen to think that the right decision was made. Wherever there's
any room for doubt, we can try something else.
the only behaviour that really makes sense and is consistent, as well as being what the community wants, is deadly edges
I have to admit, having implemented this change, I can see why deadly edges does make more sense from a design point of view; it's harder to make an edge deadly than it is to make it solid. However, from a player perspective, I mostly prefer solid. There is room for improvement, though, so...
Solid edges either allow climbers/sliders to cling onto nothing, or else require those skills to be special-cased
OK, what if we instead think of the sides as being a "one-way forcefield" rather than a solid wall, then all of the behaviour being discussed in this topic actually becomes what's
expected rather than a special case. Moreover, then, we'd let Builders turn & continue as well.
Personally, I'm now preferring this idea to "solid, but not
really". Thoughts?
WillLem made the right call in my opinion with the project instead of desperate attempts to argue for such changes in NL! 
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I would advice maybe for your old packs ... to stay with NL and for SuperLemmix make new dedicated ones with focus on using the features only SuperLemmix has!
How ironic that Icho and I are agreeing now more than ever - all it took was the existence of SuperLemmix!

Yes, I echo this entirely. SuperLemmix is there for those of us who want the features that NeoLemmix didn't want*, and content should ideally be made specifically
for it, and with its unique features in mind.
*With this said,
it doesn't mean that SuperLemmix will bring back everything that was culled/rejected from NeoLemmix! It just means that some of those discussions can be had again, from a different perspective, so perhaps with different results.
Currently, there two main ways to stop a shimmier on a ceiling, without the use of a walker ... if the shimmier encounters a wall or a gap in the ceiling. If reduce them to one (shimmier encounter a gap), I think the puzzle potential of that skill, will be reduced significantly.
Perhaps, but the skill will in turn become more interesting to use from a real-time perspective; it can be used to potentially delay a lemming indefinitely, or have them go for a pickup and then return to where they were, or - now that the Laserer has (effectively) infinite range and we have the Grenader - it could then be necessary as
part of the puzzle to create that gap to stop the Shimmier.
Imagine a designer, designing a level , where the terrain will have , several ceilings, so the player, will have to find which ones of these are the correct ones to use shimmiers. So now they will have to add small gaps , on the ceilings , that the shimmiers will be used , and in that way , revealing parts of the solution? And what , if the shape of the terrain doesn't allow something like that?
I might not necessarily be the best person to ask about level design specifics, since I'm the sort of designer that prefers multiple-solution levels and actually
likes it when a level can be backrouted (as long as the backroute is still interesting, of course!). But, to offer my two cents on the concerns you've raised here:
- Have gaps on all the ceilings to disguise the intended one
- Use Laserers/Grenaders or send other destructives in from overhead so that the necessary gaps have to be created as part of the solution
- Group pieces to create the required shape if the existing terrain pieces don't quite create the shape you need
- Use a different tileset
EDIT: Also - as will be mentioned later in this post - a Shimmier encountering a vertical obstacle less than 6px in height (but more than 2px) would attempt to traverse it, fail, and fall - so we would still have that way of getting a Shimmier down.Also , I think the loss of the "shimmier on a ceiling, arrives to wall, then it slides down that wall" combo , will be a significant one too
Agreed, and there's no reason/intention at all to lose this particular behaviour. We could simply make it "slide if they're a Slider, turn otherwise" in the same way that Climbers climb but non-climbers turn.
In fact, consider that pretty much confirmation that, if the proposed behaviour is implemented,
Shimmiers will still always prefer to transition to Slider when encountering a wall (and, of course, if they're a Slider!).
The exception to this will be level edges, for which the proposal has now basically evolved into "let's make them into one-way-forcefields rather than solid edges".
Also in the proposed change , the shimmier, will turn around, if it encounters a wall only , or this will apply , if it also , encounters small obstacles on a ceiling?
Yes, this is significant. My instinct is that it should basically be the same as for Walkers - if the obstacle is vertical, and less than 6 pixels in height, then the Shimmier attempts to continue forward, fails, and falls (where they would
ascend in the compared situation). If it's 7 or more pixels in height, they recognise it as non-traversable and turn around.
Wow, a nice juicy topic, this one!

Thoughts?