Walkthrough tips, Discussion of Campaigns [Heroes 5]

All castles except one belong to me. But Nicholas guards it. And after all the battles, I have no troops left. In total, I lost about 50,000 skeleton archers and 250 Dragons. And countless others. It would be fine if Kolya didn't reappear with an army larger than before. How do I proceed? Has anyone else managed to do it? Please tell me.

I had a similar situation, only I already owned all the Necropolis castles, but Nicholas defeated me :( Moreover, after killing Deirdre once, I was lucky enough to buy her back and equip her with necromantic troops (which was quite good). On the day when the last city became mine and Nicholas was already nearby, Deirdre teleported into it with her army, and we stood together defending it. Nick completely crushed us. First Deirdre, then me. And we couldn't switch places - he would definitely kill the first one, and we can't afford to die...
Now I had to go back to the fourth mission again, where there are still two skill slots available. I took Summoning Magic, and I was lucky: I got the Phoenix and Elemental Summoning skill, although this doesn't mean much yet... I no longer have any confidence. :(
In general, I will keep trying to complete the campaign until I realize that I have no other options. It's a pity that I got stuck like this. I've been trying to complete this fifth mission for a week now...