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

Incubi and Succubi reach full maturity by the age of 18. They cannot die of old age.

Thanks to your infernal heritage, 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 color in darkness, only shades of gray.

 As a creature of deceptive words, Concubi have proficiency with Persuasion and Deception.

You have resistance to fire and poison, but vulnerability to radiant damage.

You know the draining kiss cantrip. When you reach 2nd level, you can cast the charm person spell as a 1st-level spell once with this trait and regain the ability to do so when you finish a long rest. When you reach 8th level, you can cast the polymorph spell once with this trait and regain the ability to do so when you finish a long rest. Charisma is your spellcasting ability for these spells.

As an action you can switch between your Humanoid form and your True form. When transforming into your true form all creatures in a 30ft radius must succeed a DC 15 WIS save or be forcibly pacified similar to the effect of Calm Emotions, this effect lasts until you change into your Humanoid form or make any hostile action towards them. You are considered to be a Shapechanger or a Shapeshifter for the purpose of spell effects.

You may partially transform although this doesn't grant any extra actions, additionally you can grow wings in either form granting you a 30ft flight speed. 

When in your humanoid form, you are considered humanoid.

When in your true form, you are considered a fiend.

Certain spells and effects that specifically deal in detection will always count you as a fiend, these include Detect Evil and Good and a Paladin's Divine Sense.

You can speak, read, and write Common, Infernal and Abyssal.