Demons

Demons are biological weapons, fashioned a long time ago by wizards in an
attempt to win a war in another realm. They now run that world, which is
called Hell. There
are billions of demons in hell and more are regularly being made. Hell is
run by a central administration headed by a group of archdemons, believed to
number twelve. These are
unbelievably powerful sorcerer demons and are responsible for running hell
as well as creating most of the other types of demons.

Several of the upper echelons of demons, including archdemons, can influence
Earth, they have the ability to reach their magic across to affect things.
They use this power to make things worse where they can and often to improve
the life of those who agree to do their bidding on earth.

Demons of varying strengths are known to offer smaller bargains to benefit
people at the price of making them more vulnerable to dark influences, raising
their invitation level.

When they were first created demons were given a vulnerability to quartz in
order to make controlling them easier. While this ultimately failed, they
and their descendants still have this weakness today. Even powerful demons
may be incapacitated by a quartz stake through the chest and demonborn all
become weakened when struck by quartz weapons.