ramzez, 1. I still don't understand how you plan to cast so many spells when your Imps will drain at least half of your mana. With Keen Mind, your hero will go first, okay. The Demon Lord has a 15% chance to get Logistics; this guy can also take Keen Mind, and this leads to the second unstated problem --> 2. What will you do if the Demon goes first and happily casts Berserk on the Archers or, say, a mass Slow spell? Sure, you'll fire a Rain of Arrows with the Hive, and then the situation on the battlefield will be restored)) Hmm, and then, as a follow-up, Berserk on the Archers or Ents (let them kill your own Archers), your Knowledge will be roughly the same, and considering the Imps, you won't be able to out-magic the Demon. A couple of Rain of Arrows + an Enchanted Ballista will be enough for you, but what then?

1. A couple of scrolls with Antimagic or a Tome of Light solve the Berserk problem.
2. There is a mass Haste spell in the Attack branch to counter Slow, as I wrote. Plus, we have a horse - some of the Slow effects won't apply. Plus, either a Tent, or Luck with Magic Resistance, or Light Magic, or Shadow Seal. It's not scary at all. :)
3. If the Demon takes Keen Mind, that's good. It means he'll have to forgo Urgash's Call. :)
4. Imps. They go once, and then they are wiped out by the troops. It's rare to find someone clever enough to hide them behind a 4-tile area. Otherwise, the Dragons solve the problem. But even if he hides them, there are Archers, Druids, and Fairies. There is an opportunity to simply ignore the 4-tile area and break through to the Imps. In some cases, Demonesses can wait for one and a half turns - they are enemies and will be under the Rain of Arrows. In short, there are many ways to solve the problem; one of them will work.
5. I don't need more than two Rain of Arrows and Ballista shots. Then the troops will handle it themselves.