Empower Undead (3.5e Feat)
From D&D Wiki
 Empower Undead [Necromantic]
Undead you create are empowered with the fires of hell
Prerequisite: Able to create undead
Benefit: When you create an undead creature you may choose to add a ruby worth at least 25 gp to the material components of the spell. If you do, the undead creature gains +6 Strength. 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.