Tricky 20, no more than 1 skill assigned to each lemming
--------------------------------------------------------

1) Set RR to 70 (or around that number; more on this later) after 1st lemming 
comes out, and then back to RR 60 after 2nd lemming comes out.

2) 4th lemming out is made a blocker as soon as he lands.  See screenshot A.

3) Let the 1st lemming bash through the pillar after he moves up onto the base 
of it.  The 2nd lemming should just overtake him as he bashes through, so that 
afterwards you have lemming #2 just a little ahead of lemming #1.

4) Make lemming #2 an exploder at/very close to the position shown in screenshot
B.  The goal is for him to stop walking and explode when he is right against the
one-way-wall.  The RR change during step 1 is designed so that when the explosion
occurs, lemming #3 has just turned around from the one-way-wall, and so ends up
falling down to the edge of the explosion pit facing left.  In other words, 
we want what you see in screenshot C to happen.

5) Immediately when lemming #3 land, make him build.  See screenshot D.  Because
we made lemming #4 a blocker during step 2, you have just enough time for the
builder to connect with terrain not taken out by the explosion before lemming #5
arrives.

6) When lemming #5 gets off the builder's bridge onto the lowest part of the
explosion pit, make him bash.  The lowest part of the explosion pit is just
barely low enough to allow the basher to bash right.  See screenshot E.

7) When lemming #8 has reached the basher's tunnel, make him block at the position
seen in screenshot F, preferably a little farther to the right.  The idea is to
trap only lemming #7 to the right of the blocker, while the blocker holds back the
rest of the lemmings to the left.

8) As seen in screenshot G, once the basher has broken through and lemming #7 is
near the right edge of the bash tunnel, make lemming #7 build.

9) As seen in screenshot H, assign exploder to a lemming from the crowd at or very
close to the position shown in the screenshot.  The idea is for the exploder to
explode as close to the blocker as possible, freeing the blocker, without breaking
the left bridge.

10) The end result is seen in screenshot J.