So, a few thoughts I have on this debate.
For an intro level featuring the trick, there is
"Turnabout Sisters" from Contest #15. It would be tricky to find someone to show it to -- it would have to be someone who's played the game enough to know what the skills do -- or has never played the game before and is willing to play through introductory levels first. If I get the chance, I will try the experiment and report on how it goes.
I'm a little invested in this, since I have at least two levels that would be affected if the trick were removed. "Rhapsody in Blue" could possibly be fixed by making the blocks on the left edge of the wall steel again -- I forget why I changed them to non-steel, but it was probably to fix some other backroute. This change could result in the level having to drop a difficulty category, but that's okay. "Path of Wickedness" is more open-ended, and even though my solution does use the trick, there are others that don't.
In any case I certainly don't have the attitude that my levels must be preserved at all costs. I already had to compromise with several of my intended solutions when variable spawn interval and interrupted basher step were removed -- both far more significant changes than this one -- and we found changes that worked and saved the levels. ("Halfway Down the Stairs" even ended up as a much better level for the changes, though that was more or less by accident.)
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So, we can ignore my own levels because that's basically a non-issue. The next thing I want to discuss is tricks
in general, and that has been debated before, e.g.
Levels relying on tricks.
The first time I played
Lemmings, there were several levels where I got stuck because I needed to know a trick. Sometimes, as with "Postcard from Lemmingland" and "I have a cunning plan", I actually solved the level without the intended trick, and only learned the intended solution much later through discussing those levels on this forum. Sometimes, as with "Compression Method 1" and "No added colours or lemmings", I figured out the intended trick and solved the level.
Either way, I wouldn't say that the feeling of being stuck was a bad thing. As I said in the topic I just linked:
The initial frustration feeds into the feeling of immense satisfaction when you spot the trick and solve the level. That feeling of satisfaction when something "clicks" is the main reason why puzzle games are enjoyable.
I can report similar experiences with custom levels and harder tricks. "Attack of the Subconscious" (or its Lix equivalent, "A Matter of Perspective"). "Bipolar Maniac"/"Top Shelf". "Don't Catch Me If You Can". Each of these is centred around a single trick and can't be solved until you spot that trick. Each of these had me stumped for a long while, and was very satisfying when I solved them.
Of course, I'm just speaking from my experience here, and I accept that some players may find these particular levels, or other levels relying on certain tricks, so frustrating that there was no satisfaction, only a sense of relief at finally being past them. That's why I agree with the overall sentiment of another recent topic,
What we lack and need the most, that NL would greatly benefit from more content at an easy-to-medium range so that there's something for everyone. But I want to see us as a community
add easier content without taking away or watering down the difficult content that exists, so that everyone (including me, since I consider myself to be only a couple of notches above "novice" level) can have something to aspire to and the satisfaction of eventually -- maybe after years -- overcoming something that initially seemed unapproachable. I especially don't want us to go down the route suggested by Strato, where tricks can only be used if they are taught in pre-level text. Sometimes, pre-level text may be appropriate; but too often it spoils the experience of a level by giving away what is meant to be a puzzle.
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Finally, let's talk specifically about the digger/blocker trick. I don't have strong feelings about whether the game mechanics would be better overall if this were kept or removed. I'll leave that up to the NL and Lix developers and accept whatever they decide.
For the question of whether the trick is
discoverable by new players, that depends on several factors. One is having a "snag" -- a level one wants to solve that seemingly can't be done, so that the player is encouraged to experiement. (One reason why most of us learned this trick from discussion rather than ever figuring it out ourselves was simply that
there was no level requiring it -- it arose from a
challenge, and only a small subset of the forum were actively engaged in investigating challenges.)
Supposing the new player is confronted with a level with a snag, is it impossible they would think of trying out this trick to see whether it works? I don't think so. Anecdotal evidence suggests that for every trick, some players happen to think of it quickly and others don't -- I've already given the example of "I have a cunning plan", where some players thought up the 3-builder wall the first time they got that far when playing the original game, while I didn't think of this trick until I read about it on the forum, long after I'd finished original Lemmings. That doesn't mean I'm stupid -- it means that my mind, looking through the space of possible actions for something that would solve the level, took a route that happened to pass far from the intended trick; and since I happened to hit something else that worked, I had no incentive to keep playing the level looking for other solutions.
The hypothetical new player might already know, from other levels, that blockers turn builders and miners, so it's not much of a stretch to guess that they might turn diggers as well, and try it out to see whether it works. Sure, I'm saying that with the benefit of hindsight, even though I know that I personally didn't think of this until I read about it. I don't know, and can never know, what my experience would have been if I'd ever been faced with a level requiring this trick before I knew about it.
I do agree that it's a good idea to have a visual indicator of which way a digger is facing, and not just with respect to this trick -- sometimes it's obvious from context which direction a digger must be facing, but there are certainly times when it's helpful to know.