Draconic Presence

 
Prerequisite(s): Draconic Heritage
 
Benefit: When you cast an arcane spell, all opponents with 10' of you, that have fewer hit dice than you, get a will save vs DC = 10 + spell level + Cha modifier. If they fail, they are shaken for for a number of rounds equal to the spell level cast. If they make the save, they are immune to your Draconic Presence for 24 hours. This ability does not affect creatures with Int scores of less than 3, creatures that are already shaken or any dragons.
 
Source: Complete Arcane, Races of the Dragon