Shapechanger. The false mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Adhesive (Object Form Only). The false mimic adheres to anything that touches it. A Huge or smaller creature adhered to the mimic is also grappled by it (escape DC 13). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the false mimic remains motionless, it is indistinguishable from an ordinary object.

Grappler. The false mimic has advantage on attack rolls against any creature grappled by it.

Innate Spellcasting. The false mimic's innate spellcasting ability is Intelligence (spell save DC 18). It can innately cast the following spells, requiring no components:

At will: detect thoughts

3/day: dominate monster

Legendary Resistance (3/Day). If the false mimic fails a saving throw, it can choose to succeed instead.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 4 (1d8) acid damage.

Engulf. The false mimic engulfs a medium or smaller creature grappled by it. The engulfed target is blinded, restrained, and unable to breathe, and it must succeed on a DC 25 Constitution saving throw at the start of each of the false mimic's turns or take 10 (1d8 + 5) bludgeoning damage. If the false hydra's head moves or it's body moves, the engulfed target moves with it. The false hydra can have only one creature engulfed at a time. If the target's HP drops to 0 while engulfed, or dies, it is immediately consumed. See Grow Heads. 

Mindsong. The false mimic sings a harrowing melody which is heard by anyone within 5 miles of the head that sings. Creatures hearing the song gain gaps in their memory that they have no recollection of. If a person enters a room with a false mimic, the song may cause the person to forget the mimic was there. This is commonly used to cause people who are close to victims of the mimic to forget that person existed. 

This song does not alter reality, only perception. A woman who lost her husband may find it confusing to find men's clothes in her house as she recalls no husband. This effect does not work on people who are deaf, or are focused on the item the gap is intended to replace. For example, the women above may witness the mimic eating a man, and recall all of it during the event, but forget the second she looks away. 

As people are victims to the mindsong, they risk gaining split minds. If a victim gains split mind, the left half of the mind separates from the right. The victim does not notice this, however the left half cannot hear, thus is immune to the mindsong (but it can see). It may try to notify the victim of the false mimic, but it only controls half the body. It does not control speech. This may appear as the left hand inserting text into a note the victim is writing, or scratch letters into their chest as they sleep. Since the right brain is still impacted by the mindsong, they may never notice the letter, however the scars on their chest are harder to blank out of their mind.