This creature resembles a swirling thick pool of silvery-white mercury.
Mercury Ooze CR 4
If an opponent failed a save against the poison, one week after suffering the effects of the mercury poisoning, if the target has not received the benefits of a neutralize poison during that time span, then he must succeed on a DC 17 Will save or be affected as if by an insanity spell (caster level 10th). The effects can be removed by the successful casting of a greater restoration, heal, miracle, or wish spell.
Created by some bizarre and broken arcane experiment in ages past, the mercury ooze is a monster best left alone. The mercury ooze is about 8 feet long and 6 inches thick. It can compress its body to a thickness of 1 inch to slip into cracks and crevices.
A mercury ooze attacks by grabbing and squeezing its prey.
Mercury Ooze from the Tome of Horrors Complete, Copyright 2011, Necromancer Games, Inc., published and distributed by Frog God Games; Author Scott Greene.