Necromancer – “Invasion” [Campaign 3, Mission 3]

I also started for the third time. Not far from the teleport to the first Castle, I encountered an enemy. I was incredibly unlucky with the turn order. Usually, mages and their units go first. But in this battle, the enemy gargoyles went first, followed by my hero's turn. I cast Berserk on a horde of gremlins, which were supposed to go next. The enemy fled without firing a single shot. Then I went through the teleport and captured the city with almost no losses. At the beginning of the next week, I bought a level 18 Ogre in that city. Maybe it will be useful for something. I crossed the river to the next city.

Added after 22 hours 48 minutes
I captured three cities and gained the ability to curse cities. I decided to deal with the elf. As soon as I defeated him, a mage with 18 Titans emerged from the portal and captured the second Castle. Is this a coincidence, or a reaction to the elf's death?

In any case, I will replay from the moment I captured the 3rd Castle. You can't build high-level mage guilds in the Castles. Therefore, I will curse them immediately. If the appearance of the undead is a reaction to the elf's death, then it makes sense to gather all the undead and visit all the upgrade locations first, avoiding meeting the elf. If the mage appears independently of the elf, it makes sense to immediately run to curse the cities so that he doesn't get them.