See here for an example of the score system in SNES:
https://youtu.be/byC680Jde1gThe score seems to be based on the following:
(Saved% * 1000) + (number of skills remaining)
If we wish to expand on this, then I agree that a percentage based system should be in place for the lemmings themselves.
Regarding the conundrum of a level with minimal skills, versus a level with 50 of many skills (or even infinitely many skills available), surely the only metric worth measuring is "how many skills did the player use?"
It does not matter if the level provides infinitely many bashers. High scoring replays should be the ones where minimal skill usage occurs.
Similarly for time limits; it doesn't matter if a level has one minute or infinite time. A solution that takes 30 seconds is a better solution than one that takes 50 seconds.
What is something that needs to be taken into account is the relative weighting of all of these factors.
Suppose we have two replays, both save 100% of lemmings.
- Case A: This replay uses only 3 skill assignments, but takes 5 minutes to complete.
- Case B: This replay uses 25 skill assignments, but is completed in 45 seconds.
Which of these should be awarded more points? Which is more impressive?
Consider the following formula, with arbitrary constants inserted for example:
Score = (%Lemmings saved * 1000) - (Number of skills used * 10) - (Number of frames elapsed in replay)
Number of frames taken covers both time limit and infinite time levels. This also works in the case where a level is extremely minimal - taking less than one second. Negative scores are clamped at a score of zero.
Thus, players are incentivised to save as many lemmings as possible, whilst minimising both skill usage and time taken.
We can generally assume the frame count to be somewhat large in the case of an average level, though this particular metric is heavily biased in favour of shorter levels over longer ones.
Perhaps we could take the square root of the number of frames? Or apply some other kind of function that gives diminishing returns?
Alternatively, consider the following:
Upon spawning into a level, a lemming has a hidden "score count" variable that starts at 1000, and decreases by 1 each second that passes.
This score count decreases by some fixed amount each time a skill is assigned to that lemming. It could be something like -10 points per skill, -20 if a permanent skill is assigned.
When a lemming is saved, its score value is added to the total.
Thus each lemming contributes a different amount to the score, based on its age. Players are therefore incentivised to save lemmings as soon as possible - hastening their solutions.
This also favours solutions with fewer skill assignments too. Since these scores and their penalties are additive, then it does not matter which lemmings receive which skills.
This means that the classic "worker lemming" style levels are not penalised for having one lemming do all of the work.
There are many possible avenues for exploration here.