Loss of Lemmings: One
Make the first Lemming a Blocker as soon as it lands, such that the others land between its arms and go right. Just as a Lemming reflects, make it Dig - despite the steel, it will take a little nick out of the sandstone, and so effectively break right a little way. A dozen or so such diggers should be enough to get past the steel. Now click a normal Digger going right, i.e. before it reflects. Let it cut about halfway down the sandstone, then convert to a Basher to break out to the right. Build right just before the little step. Bash through the wood. Dig at the right end just before reflecting off the steel, and convert to a Miner after a few pixels. Destroy the blocker by either means, or wait.