You increase 1 ability score by 2 and another ability score by 1 or you increase 3 separate ability scores by 1.

Tieflings mature at the same rate as humans but live a few years longer.

Tieflings are about the same size and build as humans. Your size is Medium.

Your base walking speed is 30 feet.

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.

You have resistance to fire damage.

You know the vicious mockery cantrip. When you reach 3rd level, you can cast the charm person spell as a 2nd-level spell once with this trait. When you reach 5th level, you can cast the enthrall spell once with this trait. You must finish a long rest to cast these spells once again with this trait. Charisma is your spellcasting ability for them.

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

As a  can switch between two forms:

• Incubus/Succubus Form.  While in this form, you gain a pair of wings that gives you a fly speed equal to your walking speed. You appear more like a Incubus/Succubus. 
• Humanoid Form. While in this form, you shapeshift into a Small or Medium humanoid. You determine the specifics of the changes, including your coloration,  and hair length. You can also adjust your height and weight and can change your size between Medium and Small. You appear as a humanoid you can decide the look, you can not grow any extra appendages but you lose your flying speed and wings. You can’t duplicate the appearance of an individual you’ve never seen. Your clothing and equipment aren’t changed by this trait. 

When making a Charisma (Persuasion) or (Performance) check you gain a bonus equal to half your proficiency bonus rounded down.