Fausto Necromancer can not use god skill tome because he has spawn corpse skill. And the horn that gives your spawned units %300 damage and hp and etc. doesnt work for josephs necromancer zombies.Also doesnt work for Half demon wizard Hell Portal Skill lv 4 units.
All units get the 300% damage always some exceptions don't get the HP bonus a others bonus for them you have to drop the item and pick up again since this units are not considered summoned for the game like Worker trained units In case of Half Demon Wizard there is only a few units that don't get the HP bonus do the same with them, I'll add a text on the item to avoid confusions.
It should be using the skill normally just press the ability hotkey(X) can also see the ability if you reach level 40, I will remove the corpse ability for next version to avoid confusions and maybe add the corpse effect to another of his abilities.