I've got a few updates to this thread:
First of all, here are the results for the Shadow tribe, which nobody had ever completed for this challenge:
Shadow 1: 4 flame throwers are needed to blast through the "OZY" letters. You can get the lemmings turned around in the beginning with a bunch of fillers, which is why it's not five. In addition, you can use flame throwers to get out of the pit and get underneath the trap triggers, so fillers are not needed. Jumpers can be avoided by using the extra skills as delays for the crowd.
Shadow 2: None. The 2-skill solution from the min-skills thread uses a twister + either basher or fencer. The twister is easily avoided by waiting for all of the lemmings to come out and then using a digger at the far right edge of the holding area; he will go all the way down.
Shadow 3: 2 flame throwers + 1 roper. At least one flame thrower is needed on each side. One side can be done with three flame throwers and nothing else, which allows for either a 1-roper solution or a no-filler solution for the other side.
Shadow 4: 3 bashers + 3 glue pourers. Three walls need to be bashed; I see no way to avoid that. One glue pourer is needed to cover the bottom set of traps, one is needed to cover the gaps up top, and a third is needed to cover the top trap. The jet pack is easily avoided by using extra skills to delay the second lemming while the first lemming covers the traps.
Shadow 5: None. The min-skills solution uses just a rock climber, a jumper, and a laser blaster. Simon's earlier 4-skill solution from that thread uses a rock climber, two platformers, and a laser blaster. This eliminates the jumper. Either the rock climber or the laser blaster in Simon's 4-skill solution can be replaced with a basher, so neither of those is strictly necessary, either.
Shadow 6: 1 roper. The min-skills solution uses just 2 ropers and a superlem. The superlem can be replaced with an attractor plus one other skill, and only one roper is needed in the intended route.
Shadow 7: 1 scooper is needed to free the crowd. The digger can be replaced with the second scooper, the swimmer can be replaced with jumpers, and the jumper can be replaced with shimmiers. The rock climber can be eliminated by scooping through the wall you would normally climb.
Shadow 8: None. The min-skill solution requires a basher, bazooka, 2 platformers, and something to stop the first platformer. There also exists a left solution that uses just bashers + bazookas, so the platformers are eliminated. Bazookas are not needed in the regular (right) route, and I came up with another solution that avoids bashers:
Shadow 9: 1 roper + 1 twister should be obvious. Additional ropers can be used in place of laser blasters, and glue pourers are clearly not needed.
Shadow 10: 2 glue pourers + 2 builders. The min-skills solution uses 3 glue pourers, 3 builders, a planter, and a superlem. The superlem is easily avoided in a variant of that solution that restrains the crowd with an attractor. That same variant also allows the planter to be replaced with a builder. This leaves glue pourers and builders. I was able to get glue pourers and builders down to 2 with another solution (see spoiler):
In addition, I've identified a few other improvements:
Polar 8: None. The 100% solution avoids the exploder (obviously).
Classic 5: 1 builder + 5 bashers + 1 miner + 1 digger. The 100% solution avoids the blocker.
Classic 10: 1 builder. I was able to eliminate the climber using a hybrid of the min-skills solution and the regular route.:
First of all, here are the results for the Shadow tribe, which nobody had ever completed for this challenge:
Shadow 1: 4 flame throwers are needed to blast through the "OZY" letters. You can get the lemmings turned around in the beginning with a bunch of fillers, which is why it's not five. In addition, you can use flame throwers to get out of the pit and get underneath the trap triggers, so fillers are not needed. Jumpers can be avoided by using the extra skills as delays for the crowd.
Shadow 2: None. The 2-skill solution from the min-skills thread uses a twister + either basher or fencer. The twister is easily avoided by waiting for all of the lemmings to come out and then using a digger at the far right edge of the holding area; he will go all the way down.
Shadow 3: 2 flame throwers + 1 roper. At least one flame thrower is needed on each side. One side can be done with three flame throwers and nothing else, which allows for either a 1-roper solution or a no-filler solution for the other side.
Shadow 4: 3 bashers + 3 glue pourers. Three walls need to be bashed; I see no way to avoid that. One glue pourer is needed to cover the bottom set of traps, one is needed to cover the gaps up top, and a third is needed to cover the top trap. The jet pack is easily avoided by using extra skills to delay the second lemming while the first lemming covers the traps.
Shadow 5: None. The min-skills solution uses just a rock climber, a jumper, and a laser blaster. Simon's earlier 4-skill solution from that thread uses a rock climber, two platformers, and a laser blaster. This eliminates the jumper. Either the rock climber or the laser blaster in Simon's 4-skill solution can be replaced with a basher, so neither of those is strictly necessary, either.
Shadow 6: 1 roper. The min-skills solution uses just 2 ropers and a superlem. The superlem can be replaced with an attractor plus one other skill, and only one roper is needed in the intended route.
Shadow 7: 1 scooper is needed to free the crowd. The digger can be replaced with the second scooper, the swimmer can be replaced with jumpers, and the jumper can be replaced with shimmiers. The rock climber can be eliminated by scooping through the wall you would normally climb.
Shadow 8: None. The min-skill solution requires a basher, bazooka, 2 platformers, and something to stop the first platformer. There also exists a left solution that uses just bashers + bazookas, so the platformers are eliminated. Bazookas are not needed in the regular (right) route, and I came up with another solution that avoids bashers:
Shadow 8 No Basher
Make the first lemming a runner and the second an attractor. The runner needs to bazooka twice through the pole on the right, and then he needs to drop down the shaft using a ballooner. Once everyone has entered the level, release the crowd and make the runner fire a bazooka just before the attractor-compressed crowd splats. The blast will keep them from splatting. The remaining walls can be taken care of with bazookas and a fencer, and the rest of the level is obvious.
Shadow 9: 1 roper + 1 twister should be obvious. Additional ropers can be used in place of laser blasters, and glue pourers are clearly not needed.
Shadow 10: 2 glue pourers + 2 builders. The min-skills solution uses 3 glue pourers, 3 builders, a planter, and a superlem. The superlem is easily avoided in a variant of that solution that restrains the crowd with an attractor. That same variant also allows the planter to be replaced with a builder. This leaves glue pourers and builders. I was able to get glue pourers and builders down to 2 with another solution (see spoiler):
Shadow 10: 2 Glue Pourers or 2 Builders
Make the third lemming an attractor as soon as you can. The first lemming superlems over the first two traps, but stops before the third trap and builds over it, starting a bit to its left. Meanwhile, the second lemming pours glue, which will come to rest against the builder's bridge and cover the first two traps. Let the first lemming continue forward and lay one brick just before the water, then pour glue, which will cover the water and leave a small step to the right so the lemmings can drop down safely. From there, you can use a planter + builder to reach the exit (avoiding the third glue pourer), or you can use a jumper + glue pourer + planter (avoiding the third builder).
In addition, I've identified a few other improvements:
Polar 8: None. The 100% solution avoids the exploder (obviously).
Classic 5: 1 builder + 5 bashers + 1 miner + 1 digger. The 100% solution avoids the blocker.
Classic 10: 1 builder. I was able to eliminate the climber using a hybrid of the min-skills solution and the regular route.:
Classic 10: No Climber
Start the same way as the min-skills solution, using a builder+blocker to crawl up the left wall. One of the lemmings mines just before he exits, so that he goes underneath but the others still exit. He must bash when he is exactly five pixels below the lowest floor on the left. Meanwhile, the last lemming frees the blocker with a basher and digs down. Use three bashers to break through the wall on the right, bash twice more to drop down lower, and then mine left. As soon as he is low enough to bash underneath the steel without hitting it, make him a basher. He should just barely be high enough such that he stops bashing in the tunnel you mined earlier. From there, one carefully-placed builder gets the remaining lemmings to the exit.