Aerico

Amorphous. The aerico can move through a space as narrow as 1 inch wide without squeezing.

Carrier. If the aerico possesses someone who is afflicted with a disease, the aerico's possession action also gains the effects of any diseases of past possessed humanoids.

Innate Spellcasting. The aerico's innate spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). it can innately cast the following spells, requiring no material components:

At will: ray of sickness, infestation.

1/day each: stinking cloud, contagion.

Multiattack. Aerico uses infestation twice or makes two claw attacks.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 6 (1d4 + 4) piercing damage, and the target must succeed on a DC 13 Constitution saving throw or take 10 (3d6) poison damage. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.

Possession (Recharge 6). One humanoid that the aerico can see within 5 feet of it must succeed on a DC 14 Charisma saving throw or be possessed by the ghost; the aerico then disappears, and the target is incapacitated and loses control of its body. The aerico now controls the body but doesn't deprive the target of awareness. The aerico can't be targeted by any attack, spell, or other effect, 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.

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