Ghost

The monster can see 60 feet into the Ethereal Plane when it is on the Material Plane.

The monster can move through other creatures and objects as if they were Difficult. It takes damage if it ends its turn inside an object.

The monster makes two attacks.

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The monster casts the Etherealness spell, requiring no spell components and using Charisma as the spellcasting ability. The monster is visible on the Material Plane while on the Border Ethereal and vice versa, but it can't affect or be affected by anything on the other plane.

Wisdom Saving Throw: DC , each creature in a -foot Cone that can see the monster and isn't an Undead.
Failure: damage, and the target has the Frightened condition until the start of the monster's next turn.
Success: The target is immune to this monster's Horrifying Visage for 24 hours.

Charisma Saving Throw: DC , one the monster can see within feet.
Failure: The target is possessed by the monster; the monster disappears, and the target has the Incapacitated condition and loses control of its body. The monster now controls the body, but the target retains awareness. The monster can't be targeted by any attack, spell, or other effect, except ones that specifically target Undead. The monster's game statistics are the same, except it uses the possessed target's Speed, as well as the target's Strength, Dexterity, and Constitution modifiers.
The possession lasts until the body drops to 0 Hit Points or the monster leaves as a Bonus Action. When the possession ends, the monster appears in an unoccupied space within 5 feet of the target, and the target is immune to this ghost's Possession for 24 hours.
Success: The target is immune to this monster's Possession for 24 hours.