Necklace of (Name TBD)

Makes you Immune to Magic Damage effects (Magic, Fire, Frost, Shock), but you take Double Damage from Martial effects (Physical, Bleed, Disease, Poison).

Could also be a second one that is inverse, Immune to Martial, take double from Magic.

If Immune is too broken, try 95%. If that's too broken, try 90%. Still too broken? 75%. If that's too broken, try not to lower it below 50%.

Slowly decrease it until it's roughly balanced, while still fulfilling its purpose of basically making a person immune to half the damage types out there while making them incredibly vulnerable to the other half.

Original intent: -100% Magic/Martial damage taken, +100% Martial/Magic damage taken