Zhentarim spirit

Zhentarim spirits were the undead essence of Zhentarim wizards who met terrible ends at the hands of enemies or treacherous rivals.

Description
These semitransparent ghosts resembled spectres, often to the demise for anyone underestimating them as such. A Zhentarim spirit formed a few days after its death and appeared how it did when it was slain.

Personality
These spirits were extremely vengeful, remaining on the Prime Material plane by their sheer will until a specific task was completed or vengeance was achieved. Zhentarim spirits were only created when a powerful wizard was slain. Though they were capable spellcasters in life, a Zhentarim spirit did not have access to the spells it had once memorized.

A Zhentarim spirit would depart the Prime Material plane as soon as its killer was slain. There was no known way to trick a Zhentarim spirit by staging their killer's death.

Combat
Zhentarim spirits were not affected by things like holy water that typically had a great impact on the undead, nor could they be turned. Zhentarim spirits could become intangible or invisible whenever they wished, but needed to materialize in order to attack.

A Zhentarim spirit's strike drained the life from a target. This loss of life was permanent to the spirit's killer(s).

They were able to use an ability similar to the magic jar spell and possess others within half a mile. Only one person could be possessed at a time. The spirit needed to relinquish the possession in order to use their draining touch.

A Zhentarim spirit would reform after 100 days unless slain by a wish, finger of death, or power word, kill. With the exception of those three spells, Zhentarim spirits were immune to all other spells except magic missile and protection from evil. Enchanted weapons were needed to harm them.

History
Many believed that the formation of Zhentarim spirits was linked to the magic some Zhentarim wizards used to extend their lives.