You've already got a vampire. Hmmm.

Okay, a chimera - bat-winged monkey with the usual assortment of sharp claws and teeth, poisonous dew claws, but this one can talk and take over the bodies of others.

Formerly employed by a witch <NAME WITHHELD> but kept the livery.

It tried taking over the Warden.
Its soul leapt out.
It knows rather than let it die, the Warden picked up its soul and put it back in its body  - because it was still [i]useful[/i]....
It still has nightmares from the few glimpses it saw. It would give a demon lord nightmares.