Pale Stalker

Pale stalkers are hideous creatures resembling humans in form, but with a sickly pale pallor. The pale stalkers have sunken solid black eyes, with a single yellow dot for their pupil. When they smile, stalkers reveal a row of needle-like teeth which they use to tear apart the flesh of mortals.
Hunters from the Void. Pale stalkers are one of the few creatures able to transcend the barrier between the mortal and Abyssal realms. Pale stalkers hunt their prey from the Void, watching their movements and hunting them from afar. They seek first to possess their victims and begin to feed on them from the Void. As the creature succumbs to illness internal organ failure, the pale stalker bursts forth from the victim's flesh. In order to travel to and from the Void to the material plane, stalkers must feed. Between feedings, pale stalkers are caught in one world or the other.
Strike from the Void. Pale stalkers hunt from the void, selecting loners, vagrants, and lone adventurers. When a victim is selected for feeding, the creature will spend evenings invading the victim's dreams. They will often take the form of seductive or alluring figures, and create a sense of security and familiarity with the victim. Once the victim's subconscious has accepted the stalker's visage, they will form a physical connection between the Void and the victim's body. It isn't until the pains of being consumed from the inside become apparent that the victim is aware of the assault.

Adapted from Astral Snapper, Creature Codex (2018), pg. 43, Kobold Press

Pale Stalker CR: 3

Medium aberration, neutral evil

Armor Class: 12

Hit Points: 12d8+24

Speed: 40 40

STR

13 +1

DEX

14 +2

CON

14 +2

INT

10 +0

WIS

15 +2

CHA

8 -1

Saving Throws: Con +4

Skills: Arcana +4, Deception +4, Perception +5, Stealth +5

Damage Vulnerabilities: Radiant

Damage Resistances: Bludgeoning (Non-Magical), Slashing (Non-Magical)

Senses: Darkvision (60ft), passive Perception 15

Languages: Void Speech

Challenge Rating: 3 ( 700 XP)

Devour. If a creature is affected by the pale stalker's claw attack (see below) they must succeed a DC 13 Wisdom saving throw each time it take a long rest. On a successful saving throw, the pale stalker is ejected from the victim's body into an unoccupied space in the material plane within 10 feet of the host. The stalker is considered stunned for 1 turn after ejection.
If the creature fails their Wisdom saving throw, the stalker consumes part of the host's internal organs, reducing the victim's Constitution score permanently by 1d4 . The host dies if their CON score drops to 0. If the host dies, the stalker emerges from the corpse, tearing violently through the victim's abdomen. It becomes corporeal at that point.
While inside the host, the pale stalker has disadvantage on Wisdom (perception) checks and is considered stunned while in this state.

Actions

Multiattack. The pale stalker makes two attacks with its claws. If both claws hit the same target, the target must succeed a DC13 Wisdom saving throw or the wound becomes a rift to the Void. If a creature fails the saving throw, the pale stalker can immediately pass through, closing the rift after entering the victim's body. The affected creature is then affected by the pale stalker's devour trait.
Claws. 1d20+4 to hit, reach 5 ft., one target, Damage: 2d6+1 slashing damage.