Mage · Arcane · tier 4 · from level 25

Arcane Shielding

Rank 2/2

Decreases the Mana lost per point of damage taken when your Mana Shield spell is active by 33% and increases the resistances granted by your Mage Armor spell by 50%.

Doesn't change the damage or healing of any Mage spell.

Plan a Mage build

Averages, counting crits and misses, for a level 60 Mage with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.