Due to your deceptive nature and ability to understand when others are trying to deceive you, your Charisma score increases by 2, and your Wisdom score increases by 1.

Being too lazy or self interested to raise their own young, doppelgangers have adapted a unique reproductive cycle. As they assume attractive male forms and seduce women of a wide variety of races, before leaving them to raise their progeny. A doppelganger child appears to be a normal member of its mothers species until it reaches adolescence, at which point it discovers its true nature and is driven to seek out its kind to join them. The doppelganger will live for half the length of its mothers natural lifespan, and as a result the length a doppelganger may live varies wildly.

Doppelgangers tend towards being neutral in nature as they have no favouring of chaos over law, or good over evil. However, the nature of any individual doppelganger may be effected by their upbringing. For example doppelgangers that are raised in a chaotic environment, before reaching adolescence, may lean towards chaotic alignments. As a result seeing doppelgangers that have an alignment away from neutral is possible, but is often uncommon.

Doppelgangers in their true form range from 5 to over 6 feet tall, reaching this size at adolescence. However, due to their nature a doppelganger may appear to be any size it wishes. As long as it does not exceed the height of its natural form. Your size is Medium.

Your base walking speed is 30 feet.

Thanks to your adaptations to life in the Underdark, you have superior vision in dark and dim conditions. 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 colour in darkness, only shades of grey.

Your races natural ability to trick, deceive and charm makes it easy to spot when someone is trying to charm you. As a result you are immune to being charmed. 

Doppelgangers are born with the ability to deceive flawlessly, as a result you have proficiency in the Deception skill. 

Doppelgangers have an uncanny ability to ambush their targets. Acting quickly to seize the advantage of a well executed ambush, on your first round of a combat encounter you have advantage on attack rolls against any creature you surprise.

You have an inherit ability to change your form, as a result you can use your action to polymorph into a Small or Medium humanoid you have seen, or to revert back to your true form. Your statistics, other than size, are the same in each form. Any equipment you are wearing or carrying isn't transformed. You revert back to your true form if you die. 

All doppelgangers are masters of impersonation, thanks to their ability to read thoughts. As a doppelganger you are able to read the thoughts of a creature within 60 feet of you. Allowing you to better understand and imitate that creature, gleaming their name, desires, fears and sometimes even scattered memories. 

You can speak, read, and write Common and the language of your mothers race.