Necropolis or Castle (Which one is stronger?)

It won't work on spheres either.

Here is a link to a post containing all the information about how magic affects units in Heroes 3 (including using an artifact):
/post/89845/
Open it... download it... read it...
P.S. And here is a link to a new challenge where you can test the Berserker effect on Necromancers in practice:
/post/133838/
Essentially, by applying the Berserker buff to skeletons and other undead, you win the battle. :rolleyes: