Finally, I completed this wonderful scenario.
I played as a Warrior, because my gaming skills are quite limited. The beginning is difficult, but after capturing two castles, everything becomes easy.
First, I captured the nearest city to the starting point, belonging to the Brown faction - Ur-Ishin. I bought some troops, cleared the area. But...
First Alastor, then Nimue, Grok, Groll, and Jezebel came to attack me one after another. I successfully repelled their attacks, but lost more than half of my accumulated army. Then I hired the defeated Nimue, level 6, leveled him up, and captured the southwestern city of the Brown faction.
I mainly buffed my troops with mass acceleration and punishing strike for the simple demons, and used a few imps to absorb retaliatory attacks, while the main troops opened the gates. In general, my Agrael turned out like this:

Then I upgraded him with Skilled Machines and Rapid Fire, and also bought a ballista.
After that, everything went smoothly. Nimue repelled Grok's attacks, and Agrael captured the cities of the Brown faction:
After defeating the annoying Brown demon, I accumulated troops and went on the attack against Weyer.
Results of the battle with Weyer:
I successfully defeated Weyer and Grok, completing two quests - one for Weyer and one for his agents. After that, I went to complete the quest from the fire elementals.
Given my strength at that time, it was easy, and I easily completed this quest. The fire elementals joined me, totaling 147.
I accumulated troops and went on the attack against the Necropolis, after first checking Kaspar's army in the tavern.
I triumphantly entered the lands of Erish, and after wandering around for a few days in search of a bypass, I finally found it and, after defeating 300 bone dragons, attacked the Necropolis.

Opening the gates, mass acceleration, and my army (200 cave demons) decided the outcome of the battle.
I finished the game on the 6th day of the 4th week of the 8th month and had a lot of fun. This is the type of scenario that I really enjoy playing. Enemy raids, a small map, and a lot of creatures guarding resources and artifacts - all of this gave me a feeling of nostalgia. Especially Agrael and the demonic soundtrack.
There is no particular difficulty here. At the beginning, it's hard, but after that, it becomes easy, and Grok is just an annoying hero.
Advice: allow the upgrade of succubi and warhorses in Weyer's castle, and also allow the construction of devils. Add a fully built Stronghold to Kaspar's castle to make it more hardcore, and add some combat script (for example, at the beginning of the battle, Kaspar either casts Weakness, or Plague, or Impotence, but no more - a simple combat script with one function). It would also be possible to strengthen Grok after the Brown faction was defeated - give him more troops and another level as a buff.
And, most importantly, increase the maximum level from 18 to 26 at least. This is the most important thing.
Thank you to the author for several interesting evenings spent playing the game! I look forward to the sequel!