I got a powerful Necromancer on the fourth day. I had to replay the battle at the outpost several times. I killed 200 archers, all the vampires, and the other ghosts. After that, he hesitated and attacked my castle exactly on the 7th day. I didn't even have time to use the growth bonus.
However, he fought poorly. Despite having immense magic and mana, he constantly weakened the peasants or cast Phantom, which was easily killed by the castle (the castle is essential). And he finished the first battle with minimal losses. If he had Raise Dead, I would have been doomed!
It wasn't easier later on. 2 or 3 Necromancers with stronger armies and Raise Dead arrived. But by then, I had also leveled up and amassed an army. Ballistics helped a lot. I played with one Alaric, and Laslo was in the Sanctuary.
I took the castle, and the game ended. I didn't even go underground.
By the way, there's an exit to the upper level drawn nearby.