FYI: I will stick to the NeoLemmix term "talisman" for this post. The name "talisman" arose specifically because I was implementing a feature that I felt was achievements, but wanted to give a Lemmings-y name to it. So, if this
were to be added, it would just be additional types of talismans, from a cosmetic point of view.
Firstly, it would be weird that some packs have an achievement for completing the whole pack while others don't, at the whim of the pack's creator. If anything like this is added, I would expect all packs to be treated equally.
I don't particularly see this as being any worse than "some packs have talismans, some don't. Some give you a free one for completing the final level, some don't". Talismans have always been up to pack authors (or in more recent versions,
level authors, though this is often one and the same) to decide on exactly how they'll use; beyond things like "don't create impossible talismans" there's no particular expectations.
However, I'm really not convinced the overall effort here would be worth it. First, I'd have to outright add a means of defining, loading and tracking talismans
that are not connected to levels. Currently, of course, talismans are part of the level, which also means they're stored (both in files and in memory) alongside the level; progress is saved together with the level's progress / records; etc. So doing this would essentially be adding an entirely new thing altogether; on a
technical level it would reuse some talisman-related code in the UI and can re-use talisman graphics where needed, but the actual
logic behind it would pretty much be a completely new feature. It would indeed be correct to point out that saving / loading could be averted altogether by instead just checking the actual condition, if it's something like "beat X number of levels from the pack" or "beat every level in so-and-so rank", but the saving / loading is one of the less-messy parts anyway even if not "nothing".
There's also very limited scope to actually do anything interesting here. Pretty much anything that goes beyond "complete <quantity> levels" or "complete a few specific levels", and maybe at a stretch the pack-total or rank-total for lemmings saved, time taken or total skills used, is likely not going to see widespread use. (Note that "complete a certain rank" or "complete the entire pack" are just specific cases of the first two examples given here.) This is all on top of talismans
already being something that many players ignore.
So overall - while I do see where you're coming from, I just don't believe the benefits of this would justify the effort needed to implement it. Therefore, I'm going to reject this suggestion.
