Yes, there was indeed a 3rd demon. Yesterday, after a long break, I easily completed this mission. Well... I hired heroes with high levels so that they wouldn't fight against me later. I didn't really develop the cities. And, most importantly, I killed the red demons with Shadia. She takes them down like it's nothing. Although I tried to kill them with Raialg, but for some reason, it didn't work.
Here, tell me, friends. I've been wondering about something for a long time. How can I split, for example, 20 assassins into 10 and 10? Someone already asked this question on this forum, and they answered that you need to press Shift. But I press it, and nothing happens.
My Shadia came to this mission, having been maxed out in the previous mission, with a full set of chaos and darkness spells. Moreover, unlike Raialg, she had the Arcane Wave spell. I think she could have handled the demon as well. But she was defending the first city from enemies from the south while Raialg captured cities in the north and fought the reds.
You need to hold down Shift while moving the units. Then a menu for splitting the stack will appear.