The Dead Light is more a description than an actual name for this creature. Entirely alien in origin and thought process, the Dead Light is a predator that hunts methodically, intelligently and almost cruelly, isolating individuals and burning them to ash as it consumes them.
Largely invulnerable to earthly weapons, it can be hurt by electricity and, to some extent flame. Also repulsed by light, the Dead Light is intelligent enough to identify sources of its weakness and attempt to disable them as well as its targets’ defenses or means of escape. Severing wires, destroying car tires, burning through walls, whatever it can do to get to its next meal until day break or it is brought under control.
The metal coffin containing the creature had been discovered by a country doctor, well regarded in the area and aware of some of the less desirable elements in the lineage of the families living in the Arkham-Innsmouth surroundings. Sacrificing some of his humanity, he learned how to command the Dead Light to a small extent, giving it sustenance in the form of children who manifested mutations and traits the families did not want public.
This control was limited, however, as the command simply designated a target and returned the Dead Light back to the coffin. When the recent robbery led to its release and the death of the doctor, it resumed hunting with relish, killing the robbers and two unfortunates who had stumbled across the sad affair. Fortunately, though his sacrifice will be largely unknown, the last meal of the Dead Light that night pieced together the ritual and traded his life to return the Dead Light to its coffin. It was later buried by one of his compatriots, hopefully not to be found again.