Magic
Magic Resistance
Magic Resistance reduces what hostile magic does to you, and it is the only defence against casters that armour cannot provide. It trains by being on the receiving end, which means the only way to get good at it is to spend time being hit by spells you would rather avoid.
The only way to train Magic Resistance is to be cast at. It gains reliably while your skill is low and slows sharply once you are genuinely resistant.
At Grandmaster the skill takes 40% off every spell that lands on you. Magic Reflection stacks on top of that rather than overriding it — with the ward up, a GM resister takes 60% less spell damage, on top of the charge that eats one hit outright.