A Detrimid is a creature created by the Filth God for use in the Cult of Filth. Worthy cult members are given a detrimid to ingest. Once inside of their new host, a detrimid desolves into magical energy and seeps in. Once fully absorbed into their host, they bestow a few magical powers to them. These abilities involve summoning demons the filth god has deemed worthy, or producing filth in huge amounts.
Those who are not worthy but ingest a detrimid suffer a variety of fates. Many detrimid would poison the person from the inside, or eat a vital organ. Others might bestow slow, life draining conditions on the victim. More playful detrimids would go along with the process, but use their powers at the worst of times.
A detrimid skull is the insignia of the Cult of Filth.