The most challenging campaign.

Back when I was playing version 1.0, the third mission with Agrael (with Gilraen) seemed very difficult, but I managed to complete it, and after that, it became easier.

Now I'm replaying in version 1.6 on "hero" difficulty. In general, the "Cultist" (also known as "Cult Servant") in Railagh is indeed challenging. Perhaps I didn't level up the right abilities; I've started the campaign again to have skilled Chaos magic and level 3 luck for the "Cultist" at the beginning. If that doesn't help, I'll probably have to switch to "veteran" difficulty.