Yokai, Èmó miànjù or Demon Masks are possessed by Demons and when donned allow the Demon to possess its wearer.
The wearer is transformed into a demon, if Banishment is cast on the mask then the wearer is freed from possession.
D&D 5e
Yokia, Èmó miànjù 'Demon Mask'
Medium fiend, chaotic evil
Armour Class 18
Hit Points 68 (8d8+32)
Speed 30 ft.
STR 18 (+4), DEX 12 (+1), CON 18 (+4), INT 11 (+0), WIS 12 (+1), CHA 15 (+2)
Saving Throws STR +7, CHA +5
Skills Deception +5, Performance +5
Damage Resistances non-magical non-silvered bludgeoning, non-magical non-silvered piercing, non-magical non-silvered slashing
Damage Immunities cold, fire, poison
Condition Immunities poisoned
Senses darkvision 120 ft., Passive Perception 11
Languages Infernal, Telepathy 120 ft.
Challenge 7 (2,900 XP)Proficiency Bonus +3
Traits
Bone Blades. The demon mask can extrude blades made from sharpened bone from its wearer's hands.
Shifter. Just like the Disguise Self spell the mask can convey an at-will ability to disguise itself. An Investigation DC 17 check can be made to discover the deception.
Actions
Multiattack. Yokai, Èmó miànjù 'Demon Mask' makes two Bone Blade attacks.
Bone Blade. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8+4) slashing damage plus 7 (2d6) necrotic damage.