Fiendish Resistance Feat 5
Source Pathfinder Advanced Player's Guide
Your connection to your fiendish forebears has granted you one of their resistances as well. Choose one of the following energy damage types: acid, cold, electricity, fire, or sonic. You gain resistance 5 to that damage type.
Though you can choose any of these, the damage type typically matches a fiend associated with your bloodline. For instance, a hellspawn might choose resistance to fire, or a pitborn with a vrock ancestor might choose resistance to electricity.
Traits
Anything that doesn't list another rarity trait (uncommon, rare, or unique) automatically has the common trait. This rarity indicates that an ability, item, or spell is available to all players who meet the prerequisites for it. A creature of this rarity is generally known and can be summoned with the appropriate summon spell.
TieflingA creature with this trait is a member of the tiefling ancestry.