Mental Barrier IV

This spell functions as mental barrier III, but if you are struck by a critical hit or sneak attack, there is a 25% chance that the additional damage is negated (as light fortification). This does not stack with similar effects that negate the additional damage from a critical hit or sneak attack. In addition, you are immune to mind thrust I and II, and you take half damage from mind thrust III, IV, and V (reduced to one-quarter on a successful Will save). This spell can be undercast.