I'm suprised nobody mentioned that before, but at the time of original game Harvesters wrecked havoc! You take a shadow deck, rush your second orb and enemy is basically hopeless, forced to lose to you in economic way if he or she wants to stop this creature. There weren't much units able to counter Harvester due to his XL size, so this unit was an immortal thing, slowly butchering and stomping your armies. And believe me, there isn't any good way to interrupt your tactics.