Void Demon

Void demons are dangerous creatures found as a byproduct of the Void. They are sinister fiends hollow in appearance and hollow of spirit. They are created by fiends who are drawn into the Void where their body & spirit is leeched away by the Void itself, that leaves a spark of their previous selves present. Their link draws them to the other Planes, where they try to feed on the spirits of other creature to fill the hole in their own souls.
All void demons are grayish creatures and usually missing eyes. They absorb all light and heat in & around themselves. They are drawn to the strongest emotions & spirits they can find and are like bloodhounds to the fresh scent of it. The younger the demon the fuller it appears and regularly feed on the weakest spirits. The eldest requires stronger emotions & souls, and appears withered & weak. The latter is anything but. All void demons will torment their victims to increase the emotions of the victim's soul, and the oldest are masters of torment, though they have to syphon off more each time to feed. So much so, they have to 'feed' constantly.
Stories of these creatures go back into antiquity and are thought to have been fiends that fell from grace from the different hells in existance. With the Void being one of the oldest planes it was thought that many of these little known fiends originated from there. When a few shamans, clerics and others investigated, itr was found that they weren't, and usually there as punishments for 'crimes' in their own Planes.
It is rare to find them in the Material Plane due to the way they feed makes it obvious that something is wrong. When one is abroad the life around them are found to be weakening over time and the region becomes colder & lacking the same spark of life that is usually found. It can appear as a haunting, appearing like poltergeist activity over time but soon appearing as something worse.
In the exceptionally rare case that one is summoned, the summoner is at greater risk of having the protections in place fail as the magic is sucked out of them. Also, a portal is sometimes opened to the Void allowing for the region to become a piont of origin for this Plane to affect it for centuries or even millennia later. Even shutting down the ritual is not enough at times depending on the strength of the spells ued, and the void demon summoned.
One thing is certain once a void demon touches a place or person there is always a trace left behind. The only true way to prevent any void demon remaining in any way is to get them to go back to the Plane they originally came from. Doing this isn't as easy as it sounds.