Your Constitution score increases by 1, and your Charisma score increases by 2.

Doppelgangers are roughly the size of a tall, slender human in their normal state. Your size is medium.

Doppelgangers mature quickly, reaching maturity by their early teens, and usually live to be a couple centuries old. 

Doppelgangers tend towards the neutral alignments, although evil doppelgangers of all kinds are not uncommon. 

Your base walking speed is 30 feet.

You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

You know common and two addition languages of your choice. 

Doppelgangers are born to deceive. You gain proficiency in the Deception skill.

The Doppelganger can assume the shape of any Small or Medium humanoid, as well as any clothing or decoration on it's person (any magical equipment is copied as a mundane version) as an action. It's statistics, other than size, are the same in each form. You may not gain a fly speed in this manner, but can benefit from other physical changes such as gills or a swim speed. This form persists until the Doppelganger chooses to use this feature again or until death. This change cannot be dispelled, but can be seen through with True Seeing effects. The Doppelganger may revert to it's natural state at any time without taking an action. The Doppelganger gains advantage on all checks to impersonate a person they are currently imitating.

The doppelganger magically reads the surface thoughts of one creature within 30 ft. of it as a bonus action. The effect can penetrate barriers, but 3 ft. of wood or dirt, 2 ft. 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. You can use this feature once, regaining the ability to do so on a short rest.