Cursed Child

Shapechanger. Cursed Children can use its action to polymorph into a Small or Medium humanoid it has seen, or back into its true form. Other than its size, its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Ambusher. The Cursed Child has an advantage on attack rolls against any creature it has surprised.

Surprise Attack. If the doppelganger surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Unusual Nature. This Creature doesn't need air or sleep to survive.

Multiattack. The Cursed Child makes two melee attacks.

Claws. Melee Weapon Attack: 1d6+2 x2 Slashing damage.

Read Thoughts. The doppelganger magically reads the surface thoughts of one creature within 60 feet of it. The effect can penetrate barriers, but 3 feet of wood or dirt, 2 feet of stone, 2 inches of metal, or a thin sheet of lead blocks it. While the target is in range, the doppelganger can continue reading its thoughts, as long as the doppelganger's concentration isn't broken (as if concentrating on a spell). While reading the target's mind, the doppelganger has advantage on Wisdom (Insight) and Charisma (Deception, Intimidation, and Persuasion) checks against the target.

Puppet Strings. The Cursed Child can bind a target within a 5-foot range with invisible barbed strings. The target will then become Restrained. The target must complete a Constitution Saving Throw, if failed they take 1d12 piercing damage. The Target will lose this condition once they have either completed the game The Cursed Child plays or if The  Cursed Child's hit points become 0.