Your Charisma score increases by 2.

Aasimar mature at the same rate as humans, but they can live up to 160 years.

Dual Mind Aasimar are forced to aspire towards a Neutral alignment even if their personality may favor Good or Evil. Whether Chaotic or Lawful varies.

Aasimar have the same range of height and weight as humans.

Your base walking speed is 30 feet.

Blessed with a radiant soul, your vision can easily cut through darkness. 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 necrotic damage and radiant damage.

As an action, you can touch a creature and cause it to regain a number of hit points equal to your level. Once you use this trait, you can’t use it again until you finish a long rest.

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

Start of every day and every two hours afterwards roll a D20 for a “personality roll”; 1- 10 means the fallen personality is more prominent, 11-20 the true Aasimar persona. On 1's and 20's, there is an immediate transformation (see below for appropriate transformation) that lasts 10 minutes and leaves the character with a level of exhaustion and is unable to transform again until 1d2 day(s). During this cool down period the other personality takes over and personality rolls are not performed until cooldown is over. Transformations can be done at anytime (including when transforming into opposite personality from the current roll). Exhaustion is only gained from natural 1’s and 20’s. 

Aasimar Personality: Starting at 3rd level, you can use your action to unleash the divine energy within yourself, causing your eyes to glimmer and two luminous, incorporeal wings to sprout from your back. Your transformation lasts for 1 minute or until you end it as a bonus action. During it, you have a flying speed of 30 feet, and once on each of your turns, you can deal extra radiant damage to one target when you deal damage to it with an attack or a spell. The extra radiant damage equals your level. Once you use this trait, you can't use it again until you finish a long rest. 

Fallen Personality: Starting at 3rd level, you can use your action to unleash the divine energy within yourself, causing your eyes to turn into pools of darkness and two skeletal, ghostly, flightless wings to sprout from your back. The instant you transform, other creatures within 10 feet of you that can see you must each succeed on a Charisma saving throw (DC 8 + your proficiency bonus + your Charisma modifier) or become frightened of you until the end of your next turn. Your transformation lasts for 1 minute or until you end it as a bonus action. During it, once on each of your turns, you can deal extra necrotic damage to one target when you deal damage to it with an attack or a spell. The extra necrotic damage equals your level. Once you use this trait, you can't use it again until you finish a long rest.

DM Note: as the the PC role plays input advantage and disadvantage on personality rolls when certain actions done might lead more towards one personality than the other.