Cursed Doll

Antimagic Susceptibility. The cursed doll is incapacitated while in the area of an Antimagic Field. If targeted by Dispel Magic, the doll must succeed on a Constitution saving throw against the caster's spell save DC or fall unconscious for 1 minute.

False Appearance. While the cursed doll remains motionless, it is indistinguishable from a normal children’s toy.

Light Tread. The cursed doll barely makes a sound when moving, gaining advantage on dexterity stealth checks while unseen. It also does not take damage from great falls.

Lifeless. The cursed doll doesn't need to eat, sleep or breathe and mending cast on the cursed doll will restore 1d8 hit points.

Sneak Attack (1/Turn). The cursed doll deals an extra 10 (3d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the cursed doll that isn’t incapacitated and the cursed doll doesn’t have disadvantage on the attack roll.

Spellcasting. The cursed doll is a 6th level spellcaster. Its spellcasting ability is Charisma score (spell save DC 14, +6 to hit with spell attacks). The Cursed Doll doesn't require spellcasting components for the following Warlock spells it has prepared:
Cantrips (at will): Mind Sliver, Message, Minor Illusion
3rd level (2 slots): Arcane Lock, Catapult, Fear,  Suggestion, Hold Person Hunger of Hadar, Hypnotic Pattern 

The cursed doll regains it's spell slots on completion of a short or long rest.

Stab. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 4) piercing damage, and if the cursed doll has advantage on its attack roll the target takes an additional 10 (3d6) damage.