Homebrew Changeling Variant Species Details

Ability Score Increase. Your Dexterity or Charisma score increases by 2, and ability score of your choosing increases by 1.
Age. Changelings reach maturity within the 15th year of life and can reach ages of 70 to 90 years under good circumstances.
Alignment. Changelings tend to be mostly neutral, with most variance coming from their parent race alignments, due to their doppelganger heritage.
Size. Changelings vary between 5 to 6 feet tall usually. Your size is Medium.
Speed. Your base walking speed is 30 feet.
Darkvision. 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.
Weakened Shapechanger. As an action, you can polymorph into a Small or Medium humanoid you have seen before, or back into your true form. You can make yourself appear as a member of another race and decide what you look like, including your height, weight, facial features, the sound of your voice, coloration, hair length and any other distinguishing characteristics, but your sex. Transforming into someone else doesn't grant you their wisdom, knowledge or manners. Your statistics are the same in each form. Any equipment you are wearing or carrying isn't transformed. You can’t grow extra body parts (Like organs, limbs, tails, etc.), your basic shape stays the same. If you rouse suspicion, or if a wary creature suspects something is amiss, you have advantage on any Charisma (Deception) check you make to avoid detection. You revert to your true form if you die, lose consciousness by any means, or if you become frightened. At reaching the 6th level, you become versed with transforming and you don't revert back anymore to your true form upon becoming frightened.
Body Augments. When you use your Shapeshifter trait to transform you can augment your transformation in one of the following ways:
• You web your hands and feet gaining a swimming speed equal to your walking speed.
• You strengthen and harden a part of your form to turn it into a natural weapon such as claws, fangs, horns or other similar features. Unarmed strikes with this feature deal piercing, slashing or bludgeoning damage, appropriate to the feature, equal to 1d6 + your Strength modifier.
• You create a membrane between your arms and body that grants you a glide speed of 20.
Stealthy Movments. Thanks to the fluidity of your body and your doppelganger heritage, you are proficient in the Stealth skill.
Weakened Read Thoughts. You can cast the detect thoughts spell once with this trait, without the need for components, and you regain this ability when you finish a short or long rest. Intelligence is your spellcasting ability for this action.
Languages. You can speak, read, and write Common, the language of your parent race and one other language of your choice, your parent race can choose from.(not add manually) 
Fey Step: As a bonus action, you can magically teleport up to 30 feet to an unoccupied space you can see. Once you use this trait, roll a d20 dc10 on success you can cast again.

Changeling Variant Traits

Darkened shifter

Darkvision

Darkvision. 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.