One of my favorite stories is “At The Mountains of Madness” by H.P. Lovecraft. (Spoilers) but at the end of the story the characters run into a Shoggoth. A Shoggoth is basically a giant, GIANT ball of protoplasmic flesh constantly forming and dissolving various eyeballs, tentacles, teeth…etc.
Pretty horrifying right? But it doesn’t have to form just those organs, I’m sure it could form much much more if it applied itself. It opens the door to some truly disgusting possibilities.
I submit to you that more horrifying a giant creeping wall of eyeballs and tentacles would be a giant creeping wall of wieners and butt-holes. I can’t really thing of anything more terrifying than seeing a Shoggoth hauling ass (pun intended) after me screaming “Tekeli-li!”