@Turrican:
I've seen this glitch (self-turning blocker) work on Amiga also but have not tested it on SNES, makes sense though that it'd also work there since SNES is pretty faithful to the Amiga version. I don't know exactly how it works though. It does not work on DOS Lemmings.
As far as I know, it works as long as you assign the blocker while the lemming is standing in mid-air. The lemming will revert back to walker right away, but also somehow will turn itself around as well. It's possible this only works if the lemming was facing left before assigned blocker, I'll have to test more to see. Either way, I don't really know why that would happen. In DOS Lemmings, the center section is neutral and does not turn lemmings around unlike the left and right sections (ie. near where the blocker's arms are), so even if somehow the blocker's field of effect was not taken down right away, the lemming that reverts from blocker to walker should only collide with the center section of blocker field and not be turned around. AFAIK in SNES/Amiga Lemmings it is still the case that there is a neutral center section in the blocker's field of effect, for example if you assign a blocker to a lemming that just landed from the fall from entrance, subsequent lemmings from the entrance should not be turned around when they land exactly at where the blocker is standing. So it's still a mystery to me why exactly the glitch works on Amiga/SNES.
In the video, you'll note that the lemming was standing in mid-air when he starts building, and when blocker was assigned, the build brick has just gotten laid down but the lemming has not moved up to it yet, so the lemming is still in mid-air (ie. no ground underneath his feet) when the blocker was assigned, triggering the glitch. AFAIK the builder wasn't actually needed at all to trigger the glitch, but maybe for the overall solution it is better to do that left-facing building earlier instead of later?
On DOS Lemmings you can save all but 2 lemmings on Mayhem 10, using the sliding glitch (aka "
the wall zip trick"). The same glitch works on SNES/Amiga with a slightly modified setup to do so in that level (to account for inability to change RR while paused on those versions), I've tested it before. So chances are good that you can save all but 2 on SNES version as well, 1 more than in the video.