First of all, I drew this on the back of one of the pages of Edgar Allen Poe's prose, "A Devil in the Belfry," so you'll see the words on the other side of the paper.

The Helltula starts out as a curse, a great amount of dark energy surged into one's body where it then begins to take physical form, devouring the host. Once it has reached a certain stage of maturity, the host's body is nothing but a puppet for the creature to move with for 6 months until it has fully developed. Depending on the darkness in that host, the Helltula will take shape and get characteristics depending on their will alongwith what they have consumed. When the Helltula is fully grown, it bursts from the host body, usually taking the head with it as a sign of it's wickedness.