Between the hammer and the anvil.

Okay, it seems I placed a single guard unit in the mine, as the problem has repeated. I'll look into the skeletons. It's more complicated with the boss. The maximum level you can set for a creature is 8. You can further reduce the hero's damage by modifying the game files. But I don't know where to find those :o.

So, I've accumulated some changes for version 1.2. I'll release it with a new map, I think.