Vampiric Mist CR: 3
Life Sense. The mist can sense the location of any creature within 60 feet of it, unless the creature's type is construct or undead. Forbiddance. The mist can't enter a residence without an invitation from one of the occupants. Misty Form. The mist can occupy another creature's space and vice versa. In addition, if air can pass through a space, the mist can pass through it without squeezing. Each foot of movement through water cost's it 2 extra feet, rather than one extra foot. The mist can't manipulate objects in any way that requires fingers, or manual dexterity. Sunlight Hypersensitivity. The mist takes 10 radiant damage whenever it starts it's turn in sunlight. While in sunlight, the mist has disadvantage on attack rolls and and ability checks.
Life Drain. The mist touches one creature in it's space. The target must succeed on a DC 13 Constitution saving throw (undead and constructs automatically succeed), or it takes 10 2d6+3 necrotic damage, the mist regains 10 hit points, and the target's hit point maximum is reduced by an amount equal to the necrotic damage taken. The reduction lasts until the target finishes a long rest. The target dies if it's hit point maximum is reduced to 0.