Bes

Ethereal Sight. The bes can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.

Incorporeal Movement. The bes 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.

Possession (Recharge 4-6). One creature that the bes can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the bes; the bes then disappears, and the target is incapacitated and loses control of its body. The bes now controls the body but doesn't deprive the target of awareness. The bes can't be targeted by any attack, spell, or other effect, except ones that turn fiends, 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. While the creature is possessed, the bes uses the creature's body to violently attack any creature near it.

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