Mental Break is one of Steiner'sSword Arts. It halves a target's Magic Defense, costs 8 MP to use, and can be learned for 45 AP from the Ice Brand and Gold Helm. It has a 50% accuracy, but can be used repeatedly.
Shear is a Technick that lowers the target's Magick Resist by 10% and can be used repeatedly. No enemy is immune to it, but it has a fairly low accuracy of only 33%. Shear can be bought in Rabanastre, Nalbina and Jahara for 3,600 gil and it takes 35 LP to unlock on the License Board.
In the International Zodiac Job System version Shear costs 50 LP and can be used by the Breaker and the Archer and also the Time Mage (after acquiring Zeromus first).