Gravechill Undead (3.5e Feat)
From D&D Wiki
Gravechill Undead [Necromantic]
Undead you create are able to attack their enemies with the chill of death
Prerequisite: Able to create undead, one other Necromantic Feat
Benefit: When you create an undead creature you may choose to add a sapphire worth at least 25 gp to the material components of the spell. If you do, the undead creature deals an extra 1d6 cold damage and 1 temporary strength damage with its natural attacks. An undead created in this way counts as one Hit Die higher for the purposes of creating it and controlling it. You can only raise an undead creature's effective Hit Dice to one half your caster level through Necromantic feats.