I go back to the originals—-the monstrous shoggoths from “The Mountains of Madness”. they are black blobs with glowing green points, and can mold themselves into any organ or appendaged as ordered by the Qn’Qnx or “Old Ones”. The shoggoth had a particular way of killing, by sucking the heads off leaving the corpses headless and covered in black iridescent slime. Oh and a most pungent stench was their odor.
The “Old Ones” had yellow starfish-shaped heads and were part vegetable and supremely tough and evolved to survive most anywhere including under the sea.