"Escape to Salvation" - "Magnificent Retreat" [Campaign 4, Mission 4]

I finally finished Heroes. I played all the missions on the hero difficulty level, and I don't know why you're having trouble with Frida – it's one of the easiest battles (only Kujin and Ilaya are easier). I also didn't have any problems with Zehir, even starting from the second mission, where I maxed out his knowledge skill. The only really difficult one was Wolfenstein – in the third mission, I maxed out his absolute defense, but it turned out that without light magic, it's not very effective. If it weren't for the resurrection rune, it would have been even harder.