The problem is that there are no low-level archers. And vampires are weak without upgrades. Also, skeletons and zombies are very slow. Therefore, it's better to take two heroes. Give the skeletons and zombies to one, have them go make more skeletons, and take the mines. The second hero should quickly gather resources, especially sulfur and gems. Build and upgrade the vampires as soon as possible. And then either attack the enemy or calmly clear the surrounding area and build up your army.