Which faction poses the greatest challenge for the Dwarves?

Oh, please, don't – I have a 100% win rate against the AI on any difficulty. What made you think it was just one ghost? And have you tried playing it out to the very end? You definitely won't be able to resurrect anyone after that. And blocking with ghosts – you can block almost anyone, which is just great! Dwarves cast spells poorly because they lack magic, so a general dispel is not very effective. You can gather 2k ghosts in Random Map Generation – I've tested it. But okay, troops aren't the most important thing. I just found a recording of a battle. The opponent: Demon, level 17, 50 Dark Wyverns, 47 Kshatriyas, 14 Cyclops, 58 Wolf Riders, 149 Earth Elementals, 202 Warmachines, 22 Titans. My army: Naadir, level 22, 18 Messengers, 100 Vampires, 600 Skeletons, 15 Liches, 17 Draconians, 200 Zombies. Naadir won, losing only the Vampires, and the Draconians and Zombies were just passively defending. He won with negative spells + plague + low morale. Horrifying!

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And besides, Naadir's magic skill was only 29 – below average, I'd say. And no one even remembers the poor dwarves.