Book of shadows: Corpsecrafter - Destruction retribution

Originally from Libris Mortis 26.pg

Undead you raise or create harbor a retributive curse that is unleashed if they are destroyed.
Benefit: Each undead you raise or create with any necromancy spell releases a burst of negative energy upon its destruction, dealing 1d6 points of damage plus an additional 1d6 points per 2 Hit Dice to every creature within a 10-foot spread (dexterity DC 15 half). This damage comes from negative energy.