Crimson Mist

Pseudocorporeal. The crimson mist is weightless and can enter a hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing.

Sanguine Feast. Whenever the crimson mist deals necrotic damage to a living creature with blood in its body, the creature's hp maximum is reduced by the same amount and the mist regains hp equal to half the necrotic damage dealt. The reduction lasts until the creature finishes a long rest. The creature dies if this effect reduces its hp maximum to 0.

Vampire Weaknesses. The crimson mist has the following flaws: Forbiddance. The crimson mist can't enter a residence without an invitation from one of the occupants. Harmed by Running Water. The crimson mist takes 20 force damage if it ends its turn above or within running water. Sunlight Hypersensitivity. The crimson mist takes 20 radiant damage when it starts its turn in sunlight. While in sunlight, it has disadvantage on attack rolls and ability checks.

Engulf. The mist moves up to its speed. While doing so, it can enter a Medium or smaller creature's space. When the mist enters a creature's space, the creature must make a DC 15 Dexterity saving throw. On a successful save, the creature can choose to be pushed 5 feet back or to the side of the mist. A creature that chooses not to be pushed suffers the consequences of a failed saving throw. On a failed save, the mist enters the creature's space, and the creature takes 15 (4d6) necrotic damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 15 (4d6) necrotic damage at the start of each of the mist's turns. When the mist moves, the engulfed creature doesn't move with it, and is freed. An engulfed creature can try to escape by taking an action to make a DC 14 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the mist. A creature within 5 feet of the mist can take an action to pull a creature out of the mist. Doing so requires a DC 14 Strength check, and the creature making the attempt takes 14 (4d6) necrotic damage. The mist can only engulf one Medium or smaller creature at a time.