Shapechanger. The morphic doppelganger can use its action to polymorph into a Small or Medium humanoid 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. It reverts to its true form if it dies.

Ambusher. The morphic doppelganger has advantage on attack rolls against any creature it has surprised.

Surprise Attack. If the morphic 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.

Morphic-Blades. The doppelganger can use an action to shift both if its arms into steel-like blades that can be used as Shortswords. While being used in this manner the morphic doppelganger can use its bonus action to make an additional Morphic-Blade attack on its turn.

Multiattack. The morphic doppelganger makes two melee attacks.

Morphic-Blade. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage.

Read Thoughts. The morphic 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 morphic doppelganger can continue reading its thoughts, as long as the morphic doppelganger's concentration isn't broken (as if concentrating on a spell). While reading the target's mind, the morphic doppelganger has advantage on Wisdom (Insight) and Charisma (Deception, Intimidation, and Persuasion) checks against the target.

 If the morphic doppelganger previously used its Morphic-Blade ability, it can use its Morphic-Blade attack as a bonus action on its turn.

Morphic-Blade. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage.

Morphic-Appendage. An additional appendage bursts forth from the morphic doppelganger's body in response to an incoming attack.

The morphic doppelganger can use its reaction to reduce income damage from a melee or ranged weapon attack as part of the creature's body reacts to mitigate the threat. When it does so, the damage it takes from the attack is reduced by 11 (1d10 + 6) damage of the same type which was dealt.

The morphic doppelganger can take a single legendary action, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The morphic doppelganger regains spent legendary actions at the start of its turn.

Shapechanger. The morphic doppelganger can use its legendary action to polymorph into a Small or Medium humanoid 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. It reverts to its true form if it dies.

Recharge reaction. The morphic doppelganger can use its legendary action to recharge its reaction to use. This can only be used if the morphic doppelganger has already expended its reaction earlier in the same round.