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2020-11-26 23:13 dustin  
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it should even be possible with 3 fireflies ;D

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2020-11-27 12:56 nesdori  
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it indeed is possible with 3 flies and there are actually many possible gap combos to achieve that. it's possible to solve this cave by either smashing all boulders or leave one.  
also a fly can be 1 gap ahead of standard flow because it will just kindly wait for a falling boulder without changing direction for one frame.  
  
here is a list of all possible gap combos to smash all boulders with 3 flies. the first fly needs to hit a boulder when there's already another boulder in the pit.  
  
2+2+2 combos (each fly explodes two boulders):  
  
6-7  
6-8  
7-6  
7-7  
  
to smash all but one boulder, one of the flies have to hit a boulder without another boulder being in the pit. here are all the possible gap combos to that.  
  
if the first fly hits a boulder without another in the pit the possible gap combos for the remaining flies are of course then the same as when smashing all boulders):  
  
1+2+2:  
6-7  
6-8  
7-6  
7-7  
  
then combos where the first fly hits a boulder when there's another in the pit:  
  
2+1+2:  
  
4-7  
4-8  
5-6  
5-7  
  
2+2+1:  
  
6-5  
6-6  
7-4  
7-5  
  
so 12 different unique gap combos to solve this with 3 flies and 16 different actions because with 6-7, 6-8, 7-6 and 7-7 two different timings to hit the first fly can be used. and of course numerous combos to solve with all 4 flies; i'm not going to cover them :)  
  
so i wonder: which combo is the fastest or easiest to create. i haven't decided yet.. :)

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2020-11-27 13:43 nesdori  
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ok now i realized few things. a direct hit to the first fly without a boulder in the pit is not possible because rockford has no time to evade the explosion. so 1+2+2 is not possible. it still leaves 12 gap combos from previous list and of course it's also possible for the first fly to be one frame ahead which increases the amount of possible gap combos. it doesn't double it because now some gaps can be used in two ways in the same group: either all flies are one frame ahead or none is. this leaves 7 different possible gaps per group:  
  
2+2+2:  
  
6-7 -  
6-8 -  
7-6 -  
7-7 -/+  
7-8 +  
8-6 +  
8-7 +  
  
2+1+2:  
4-7 -  
4-8 -  
5-6 -  
5-7 -/+  
5-8 +  
6-6 +  
6-7 +  
  
2+2+1:  
6-5 -  
6-6 -  
7-4 -  
7-5 -/+  
7-6 +  
8-4 +  
8-5 +  
  
if a gap has "-" the first fly must not be delayed by a falling boulder for that gap to work. if "+", it must be delayed. if "-/+" the gap works with either way. now some gaps are present in multiple groups with different delay strategy. 6-7 can be used to get 2+2+2 without first fly delay and 2+1+2 with delay.  
the are two gap combos in each group which are present also in other groups with different first fly delay. this leaves 18 unique gap combos which can be used to solve this cave with 3 flies. i hope i got it right this time :)

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2020-11-27 15:02 shredder  
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thanks for nice analysis  nesdori  :)   
my run with 4 ffs with 5-free space gaps between each one.

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2020-11-27 23:41 shredder  
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ok, improved run with 3 ffs ;)

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2020-11-29 18:20 dustin  
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very good, both  nesdori 's theory and shredders practice! :D