The Mimic Demon is briefly mentioned in The Warded Man and fully appears in The Desert Spear, The Daylight War, The Skull Throne, and The Core. It has the power to imitate inanimate objects (like ice and stone) and living beings, but is only seen to use its power on demons, humans, and one rodent. The mimic can become a perfect copy of whatever the mimic demon wants it to, it can imitate the appearance and even the voices of humans. It can take almost any demon form and copy its abilities. Mimic demons are also bodyguards to the Mind Demons and are linked with the same mind demon for its lifetime. The demon loves to inmate the voices of parents to lead their child to death or worse.
The most powerful Mimic Demons can use multiple different demon attributes at the same time. They prefer to attack using tentacles to pierce and strangle. Defensively they prefer to use parts of Rock Demons, but can also use
In some cases a Mind Demon can actually be completely enclosed by a Mimic Demon while it controls it, such that the Mimic must be penetrated to get to the Mind Demon.