Apex Doppelganger

Shapechanger. The doppelganger can use its action to polymorph into a Small or Medium humanoid or an environment it has seen, or back into its true form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. When the doppelganger hides in an environment that it has polymorphed into, it gains advantage on Stealth checks. It reverts to its true form if it dies.

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 12 (4d6) damage from the attack.

Multiattack. The doppelganger makes three melee attacks.

Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 9 (1d10 + 4) bludgeoning damage.

Breath Taker. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 [rollable](1d12 + 4) piercing damage, and the target must make a DC 14 Intelligence saving throw, taking 3 (1d6) psychic damage on a failed save or half as much on a successful one. On a failure, the target also looses the ability to form understandable words and make loud vocal sounds until the end of this creature's next turn. Affected targets cannot cast spells with verbal component (V).

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.

Cunning Action. The Doppelganger Assassin can use it's bonus action on each of its turns to take the Dash, Disengage, or Hide action.

Minder Reader. The doppelganger coordinates his evasive maneuvers with its Read Thoughts ability to dodge all attacks from the target. Dodged attacks impose disadvantage on the attacker.