D&Dtools1

Benefit

You gain the frightful presence special ability with a radius in feet equal to 5 × 1/2 your racial Hit Dice.

The ability takes effect automatically whenever you attack, charge, or fly overhead. Creatures within the radius are subject to the effect if they can see you and have fewer Hit Dice than your racial Hit Dice.

A potentially affected creature that succeeds on a Will save (DC 10 + 1/2 your racial HD + your Cha modifier) remains immune to your frightful presence for 24 hours. On a failure, creatures with 4 or fewer Hit Dice become panicked for 4d6 rounds and those with 5 or more Hit Dice become shaken for 4d6 rounds. Dragons ignore the frightful presence of other dragons.

Special

If you have both this feat and you have (or later gain) the frightful presence ability, your frightful presence radius either increases by 50% or increases to 5 feet × 1/2 your racial Hit Dice, whichever figure is higher. The save DC against your frightful presence also increases by 2.