Do not worry if one of your characters dies; they will come back to life after you finish the episode. However, to make sure you have a nearly 100% chance of winning, get on top of the roofs when no monster is there. Once this is done, you can snipe away at your enemies. After you shoot, go all the way back to the mountain that touches the roof, but do not go down. Shield, because the monsters will shoot your building. If you are all the way back, you will not get hurt. Do not worry -- the building cannot crash and you will be fine doing this.