rot flesh dragon

a symbiotic life form
incredibly territorial and protective of host. it invokes a state of constant cannibalistic hunger and drives its host to devour any person they see. it often bonds with vengeful or lonely people. often seen with red rotting flesh, however does have skin which can grow and cover it or dissolve depending on mood.
first form: serpent. sends out small flesh worms to gather blood from eating fish and small animals. burrows through snow to use as cover. it bonds with a chosen host when they have finally devoured enough biomass.
second: flesh cloak. wings and ribs cover host like a cloak. provide protection from sunlight. attacks with swift flight attacks and sharp teeth by separating from host briefly before returning. host develops some sense of thought besides predatory hunger.
third: full symbiosis. can now move and act independently of host. very large. host develops the ability to think for themselves besides a sense of constant hunger and/or loneliness

(I based this on a dream I had)