I suggest giving him the "Undead" ability, since he's one-third Herald, so he wouldn't care about the Attack Rating penalty, or increase his initiative and speed, or increase his HP fivefold.
I also found a flaw: in the Orcish lands, the Prophet asks for 2 artifacts guarded by Helmar and Garuna. However, I already had both of these artifacts, even though I didn't fight either of them, because the map has 5 artifact shops (2 near Sha'hadir, where the undead roamed, and 3 more can be built in the academic cities). Either remove the shops from the map altogether, or change the quest so that you have to kill neutral creatures, or capture an Orcish city, or something else.