Walkthroughs for custom maps.

Xaart, I opened your save file in two different folders with my "Heroes" installations (separately - "The Shadow of Death" with WoG installed, and separately - a clean "Complete Collection"). In both cases, the Berserk skill is present in Gandalf's spellbook. I've attached proof. So, it seems like there's something wrong with your version of "Heroes." Maybe you should try a different version from a different source? It's possible that while playing on some other map, some game files were replaced (there are such maps, I don't play them to avoid any misunderstandings with others).