Level 11: Keep your hair on Mr. Lemming[edit]
The challenge here is that you can only bash through the one-way wall in the direction of the arrows. Make two lemmings climb up the wall, and then have them float down the other side. The first one should block before he goes in the exit, turning the second one around. Make this lemming bash through the wall in the direction of the arrows. Blow up the blocker to clear the path to the exit.
Level 12: Patience[edit]
Make the first lemming bash through the big wall in the center of the level. Several lemmings will turn around and head back to the left. Use a blocker near the edge of the cliff to keep them from falling off. The lemmings will eventually amass in a pit. Use bridges to get them out of this pit and into the exit.
Level 13: We all fall down[edit]
This is the first (and easiest) of four levels over the course of the game with the same layout and the same title. Make the first lemming dig just before he falls off the platform. Do the same for the other lemmings, as well. The trick here is that the small difference in height between the top and the bottom of the platform prevents the lemmings from dying upon hitting the ground below.
Thankfully, this level was omitted from Lemmings For Windows. What a pity the other three versions weren't also omitted...
Level 14: Origins and Lemmings[edit]
Make the first lemming bash or mine through the pillar to the right of the entrance. Use bridges to get about a quarter to halfway up the next pillar and then bash from the very top of the bridge. Repeat this process for the next section and you should be able to reach the exit with 100%.
Level 15: Don't let your eyes deceive you[edit]
Make the second lemming block once he drops down to the ground, before he reaches the staircase leading to the first pillar. The lone lemming ahead will blaze a trail for the others to follow later on. Begin by bashing through each of the three pillars. Use 4-5 builders to get over the large pit (when the lemming shrugs his shoulders, he's out of bricks and you need to give him more). Also use 2 builders to patch up the hole in the stairs leading to the exit. When the lemming is finished, remove the blocker (this can be done by mining away the ground he stands on, then changing the miner to a builder) to allow the others to follow.