This gives the Demi-hero magic resistance, similar to the resistance that level 6+ creeps have. Namely, you can't be Polymorphed, Possessed, etc, and all offensive spells have a shorter duration on the target (such as stuns, Ensnare, etc). It DOES NOT reduce damage dealt to the target, however. That’s an effect of hero armor, not hero magic resistance.
Gives Demi-heroes increased resistance to spell damage.