However, the description you gave made me go and look up my mythos guides
Here is what I found:
Gnome
The description of an ugly thing small but able to move fast in the darkness made me think of either a gnome or a spriggan. Gnomes are no punishment for your actions. They just happen.
A race of small, misshapen, dwarf-like creatures that dwell in the earth. The name 'gnome' was given to them by the medieval scholar Paracelcus, in an attempt to describe the most important of the earth spirits. Gnomes live under the earth, where they guard treasures. According to Paracelcus, they move as easily through the earth as humans walk upon the ground. They cannot stand the light of the sun, for even one ray would turn them to stone. Some sources claim they spend the hours during daylight as a toad. They are in some way related to goblins and dwarfs.