Unremembered Demon

Incorporeal Movement. The demon can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 17 (4d6 + 3) necrotic damage.

Possession (Recharge 5-6). One humanoid that the demon can see within 5 feet of it must succeed on a DC 15 Charisma saving throw or be possessed by the demon; the demon then disappears, and the target is unconscious and loses control of its body. The demon now controls the body. The demon can't be targeted by any attack, spell, or other effect, except ones that affect demons specifically, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the demon ends it as a bonus action, or the demon is forced out by an effect like the dispel evil and good spell. When the possession ends, the demon reappears in an unoccupied space within 5 feet of the body. The target is immune to this demon's Possession for 24 hours after succeeding on the saving throw or after the possession ends. 

Eat Name. The demon may devour the name of a victim it has possessed. Each turn, as an action the demon may spend its entire turn to inflict 1 hit point of damage and devour one point of intelligence.  If the target reaches 0 hit points, the demon devours the name of the victim. The victim may not be resurrected by any means. 

When the name is devoured, all they have ever written or created as well as anything created in reference to them vanishes from the world, leaving only blank spaces, muddled images, and fuzzy memories where their works and traces of them once were.  Their descendants and relatives remain, time is not rewritten to exclude them, but memories of the name-eaten parent or spouse fade away entirely. 

Even magical writing, such as spells they have written down or invented, devil contract signatures, tattoos, or memories of their name or works are affected.  Upon consuming a victim's name, the demon vanishes back to the Abyss leaving a withered husk of a corpse behind. Any healing, protective, or restorative magic will cast the demon out early, ending its possession. If this occurs, damage may be healed normally. The intelligence damage is healed after a long rest. No other ill effects remain. If the demon dies, any name it has eaten within the past 24 hours before its death is restored. 

Destroy Knowledge (At Will). The demon touches one object upon which some form of deliberately placed information has been recorded in some fashion. All information is tracelessly erased from the targeted object. The demon cannot erase magical writing this way.  Artifacts and greater items are unaffected. If the demon dies, any information it has erased within the past 24 hours before its death is restored. Otherwise only a Wish spell or the act of a god of knowledge or secrets can restore the information on an object erased by the demon.