The Slenderman

Sickening Aura. The Slenderman gives off a aura of otherworldly power that makes individuals violently ill. The aura has a range of 100ft. Any creature(s) caught inside of it must make a DC 22 constitution saving throw or rake 1 level of exhaustion. The creature(s) can remake the saving throw to end this effect. If they fail they take an additional level of exhaustion. 

Teleport. The Slenderman can cast the misty step spell at will without expending a spell slot or any components. 

Spellcasting. The Slenderman is a 10th-level spellcaster. His spellcasting ability is Charisma (spell save DC 22, +16 to hit with spell attacks). The Slenderman has the following Sorcerer spells prepared:
Cantrips (at will): chill touch, message, mind sliver, friends 
1st level (4 slots): charm person, disguise self, sleep. 2nd level (3 slots): blindness/deafness, crown of madness, suggestion. 3rd level (3 slots): fear, hypnotic pattern, major image. 4th level (3 slots): confusion, greater invisibility, blight. 5th level (2 slots): dominate person, creation.

Multiattack. The Slenderman can make two attacks on his turn, one with his tendrils and one unarmed strike

Tendrils. Melee Weapon Attack: +16 to hit, reach 10 ft., 1 target. Hit: 20 (1d10+ 10) bludgeoning damage. 

Unarmed Strike. Melee Weapon Attack: +11 to hit, range 5 ft., 1 target. Hit: 13 (1d8 + 5) slashing damage.

Defensive Teleport. As a reaction on his turn, when Slenderman takes damage, he can immediately teleport a distance equal to his movement speed away from the attacker to any unoccupied space.