Critical Spell Surge

Due to the high natural magical energy in Merisyl, spells will sometimes "surge", causing critical damage. 

Roll a d20 to determine whether or not your spell surges.  On a natural 20 your spell spell will (if not resisted) result in a doubled effect (for example, double damage or double duration).

The base chance can be altered by some magic items or feats (such as Surge Affinity).