Damage Transfer. While possessing a creature, the voider takes only half the damage dealt to it (rounded down), and that creature takes the other half.

False Appearance. While the voider remains motionless without its underside exposed, it is indistinguishable from a shadow.

Spellcasting. The voider is a 11th level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +6 to hit with spell attacks). The voider has the following Sorcerer spells prepared: 

Cantrips (at will): [blade ward], [mage hand], [mind sliver (UA)]

1st level (4 slots): [charm person],[expeditious retreat], [magic missile], [shield] 

2nd level (4 slots): [darkness], [phantasmal force], [see invisibility]

3rd level (3 slots): [blink], [fear], [slow] 

4th level (3 slots): [confusion], [dimension door]

5th level (2 slot): [telekinesis]

6th level  (1 slot): [mental prison]

Moan. Each creature within 60 feet of the voider that can hear its moan and that isn't an aberration must succeed on a DC 13 Wisdom saving throw or become frightened until the end of the voider's next turn. If a creature's saving throw is successful, the creature is immune to the voider's moan for the next 24 hours.

Mind Blast (Recharge 5–6). The voider magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 22 (4d8 + 4) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Possession (Once per day).  The voider can possess a creature if they drop below 75% of their hit points. The creature must roll a DC 15 Wisdom save. If the creature is frightened, incapacitated, stunned, or unconscious, they have disadvantage. A failed save results in the consciousness of the creature trapped in a mind prison. The voider can automatically possess an unconscious creature. The possession lasts until the creature breaks out of the mind prison or until the voider gives up the possession. 

Dimension door can be used as a reaction once per day.