Copies

Shapechanger. The doppelganger can use its action to polymorph into any creature, humanoid figure or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying is transformed. It becomes a fleshy goo upon death.

Ambusher. The doppelganger has 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.

Multiattack. The doppelganger makes three melee attacks.

Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage.

Read Thoughts. Copies magically reads the surface thoughts of one creature within 10 feet of it. The effect can penetrate barriers. While the target is in range, the doppelganger can continue reading its thoughts. While reading the target's mind, the doppelganger has advantage on Wisdom (Insight) and Charisma (Deception, Intimidation, and Persuasion) checks against the target.

Copies will polymorph into any creature it has seen and gains its stats and characteristics. if provoked Copies will morph into their chosen attack form. They will constantly change throughout the course of the battle to confuse the attacker.