Blood Bound Spirit

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

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

Rejuvenation. If it's altar still exists a destroyed spirit's essence will regenerate in 24 hours, regaining all its hit points and becoming active again. The new spirit appears within 5 feet of it's altar

Legendary Resistance (1/Day). If the spirit fails a saving throw, it can choose to succeed instead.

Multiattack. The spirit makes two withering touch attacks.

Withering Touch. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 17 (4d6 + 6) necrotic damage.

Etherealness. The Spirit enters the Ethereal Plane from the Material Plane, or vice versa. it is visible on the Material Plane while it is in the Border Ethereal, and vice versa, yet it can't affect or be affected by anything on the other plane.

Horrifying Visage. Each non-undead creature within 60 feet of the spirit that can see it must succeed on a DC 16 Wisdom saving throw or be frightened for 1 minute. If the save fails by 5 or more, the target also ages 1d4 × 10 years. A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to this spirit's Horrifying Visage for the next 24 hours. The aging effect can be reversed with a greater restoration spell, but only within 24 hours of it occurring.

Possession (Recharge 6). One humanoid that the spirit can see within 5 feet of it must succeed on a DC 16 Charisma saving throw or be possessed by the spirit; it then disappears, and the target is incapacitated and loses control of its body. The spirit now controls the body but doesn't deprive the target of awareness. The spirit can't be targeted by any attack, spell, or other effect, except ones that turn undead, and the spirit retains it's alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. The spirit 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 spirit ends it as a bonus action, or the spirit is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the spirit reappears in an unoccupied space within 5 feet of the body. The target is immune to this spirit's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

Psychic Wail(recharge 5-6) The spirit magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 16 Wisdom saving throw or take 22 (5d8) psychic damage and be stunned for 1 minute. The stunned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Devour Memory. The spirit touches one incapacitated creature and chooses 1 hour from among the past 24. Unless the creature succeeds on a DC 16 Intelligence saving throw, the creature loses all memory of that hour. If the creature fails the save by 5 or more, their hp becomes 1. The creature regains the memory only if the the spirit dies within the next 24 hours.

The Blood Bound spirit can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. the spirit regains spent legendary actions at the start of it's turn.

Move. The spirit moves up to its speed without provoking opportunity attacks.

Withering Touch. The spirit Makes one withering touch attack. 

Etherealness (costs 2 actions). The spirit moves into the ethereal plane or back to the material plane.