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. Every spell teaches you something up to 50, and from there it slows sharply: the second half is most of the climb.
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.
Blackrock plate adds to it as well: 1% off a landed spell for every piece you wear, 7% for a full suit and its shield, in the same total rather than a separate one — a GM resister in full Blackrock with Magic Reflection up takes 67% less. Magic Reflection, a Twinheart Seal, the Gate of Spellward and the armour all add into that one reduction, and the whole of it stops at 80%.