Lemmings 3D Mayhem
Mayhem 61 - 8 skills (7 skills on "can't live without" and I can't figure out a way to simultaneously eliminate the remaining two)
Mayhem 62 - 13 skills
Mayhem 63 - 6 skills
Mayhem 64 - 8 skills
Mayhem 65 - 10 skills
Mayhem 66 - 7 skills
Mayhem 67, I've confirmed two different paths for 6 skills (one via middle spring, one via first spring), but I'm working on a possible 5 skill solution. Best attempt so far saves 59 (and would save 60 but for a minor screwup near the end), but a lot of lemmings are lost to a different spring and I think there's room to avoid this with better RR manipulation (and that's saying something, as this solution already involves over 20 release rate changes).
EDIT: Yeah, okay, I've had enough of trying to make this work, at least for now. I'm 100% sure it's possible, but trying to adjust the release rate via modifying the replay file breaks everything else (as is often the case in L3D - replays don't like being modified, or having their levels modified), and trying to do it manually - even with DOSBox set to run at really low cycles - is just impractical, due to the reactions needed, as well as how difficult it is to hit any given specific value.