New era.

I can give you the save file right before the battle. Of course, I recruited Kane and Zehir during the Walkthrough. Frida's specialization doesn't work very well, and when you need to resurrect large losses, it just gets in the way. The Tome of Darkness isn't really needed, as the Castle has all the necessary spells. Unless, of course, you want to cast it before the next demon to make Subordination available as an option. But the next one is killed by paladins with Vampirism; the main thing is to cast it in time.

You practically need to re-spec before each demon, as they all have their own strengths and weaknesses, and they don't forgive mistakes.
The same goes for logistics; while it's generally needed on the map, it's definitely not needed in battle. Besides this demon, there will be another one on the surface and the final one in the Dungeon, so you definitely shouldn't neglect developing Rai'lag. You need to approach his development very carefully.

Thank you, I understand. I watched your battle recording and I have to say that you are incredibly lucky. I've been trying different combinations for two hours now, but to no avail. I followed your build, tried 15 times, but it didn't work. I decided to invest in Leadership instead of Education after gaining mana, but that didn't help either. Only two scenarios happen; in one, they cast Subordination on me constantly, which I can't remove, and then I die. In the second scenario, things are easier; I've been spamming it for the last hour, but it still doesn't work. In the first turn, I can't cast Berserk on anyone, nor can I give Vampirism to the horses; the spell is canceled, and Slow and Dispel are triggered. In the second turn, I can cast Berserk or give Vampirism to the horses. I've tried both many times, but the outcome is always the same. The opponent's Luck triggers every time; they get 2-3 turns under Morale and just destroy me. I have 7 Luck, but even that isn't enough to withstand such an onslaught. Overall, I managed to defeat everyone except the Demoness, Lords, and Demons once. And at this stage, he starts attacking only with Demonesses, while these two stand in defense and don't attack me))) so, I'm not very lucky