Juiblex the Devourer

Called the Faceless Lord and the Oozing Hunger in ancient grimoires, Juiblex is demon lord of slime and ooze, a noxious creature that doesn't care about the plots and schemes of others of its kind. It exists only to consume, digesting and transforming living matter into more of itself.
A true horror, Juiblex is a mass of bubbling slime, swirling black and green, with glaring red eyes floating and shifting within it. It can rise up like a 20-foot hill, lashing out with dripping pseudopods to drag victims into its bulk. Those consumed by Juiblex are obliterated.
Only the truly insane worship Juiblex and tend to its slimes and oozes. Those who offer themselves up to the demon lord are engulfed by it and become vaguely humanoid, sentient oozes. The bodies of these former flesh-and-blood creatures form Juiblex's extended physical body, while the demon lord slowly digests and savors their identities over time.