Gemstone hidden in the body of an undead fey sprite who was previously my halfling cohort.
It was her heart, basically. Her animus. I bound a similiar gem in each of my major lieutentants.
Brutus, the Fast Zombie Bulette who I used as a PC APC or to quickly offload a few dozen skeletal soldiers in the thick of battle or just MANGLE what I pointed him at.
Renard, The Dread Knight, who was my personal body guard and the past master of the knights templar before he tried to abscond with my dignity. Would ride into battle on the back of Brutus.
Zephyr, the giant intelligent skull of a hydra, animated by a combination of necromancy, and priestly power. Imbued with an abundance of negative energy, and that of Quetzalcoatl the serpent god.
Zephyr was the least imposing of the bunch, but commanded the skull legion. ~20-50 flying belching skulls. 1d6 elemental damage with an attack bonus of about +6. Good for large engagements, less so against singular tough enemies.
The party frequently stated I would make a much better bbeg than our current bbeg.
Then it turned out that our current bbeg was me, after the loss of my phylacteries, and a time travel mishap.
Necromancy. Not even once.