I have a goo demon OC, he is a muck demon specifically, he finds a host and makes them addicted to smoking, drinking and drugs, as well as unhealthy foods so he can devour the toxins created from it.
While this parasite will lengthen your lifespan, your life will be down spiral rapidly, eventually your inner organs will be patched up and eventually replaced with his muck until there is nothing left of you but an empty husk.
I drew this one for valentines day, he has a couple fans among my friends xD
This is him when he is walking around without a host, or when the host prefers him to appear.
He goes by 'he' but has no genitalia, belly button or nipples (huehue)