Add +1 to your Constitution ability score.

Thanks to your demonic powers, 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 can speak, read, and write Common and Abyssal.

If born from a polymorphed demon and a non-demon humaniod, a Half-Demon takes on the size of its non-demon parent race. After birth, a Half-Demon usually grows to become larger than the other members of its non-demon half.

If created from a magical transformation, a Half-Demon body can grow larger in a short amount of time.

Half-Demons created through reproduction can be good or evil depending upon their experiences and how they are raised. Half-Demons created by magic can be corrupted by their transformation, if they were not already evil. Half-Demons tend to be chaotic for their souls contain great energy and chaos, though a Half-Demon can learn to control their inner chaos.

Half-Demons tend to live longer than those related to their non-demon side by about two-hundred years. However, they mature at the same rate as those related to their non-demon side.

Your base movement speed is 30.

As a bonus action, Half-Demons can summon a soul weapon that shares the same chaotic energy of their soul. It can deal fire, lightning, cold, thunder, necrotic, or force damage depending on what their soul contains. Your soul weapon can take the shape of all simple and martial melee weapons, yet you may only change the form of your weapon once per long rest. Your soul weapon deals fire, lightning, cold, thunder, necrotic, or force damage equal to that of the weapon it imitates + your Charisma Modifier. The attack bonus for your soul weapon attacks is your Charisma Modifier + your Proficiency Bonus. If your grasp is released from your weapon it will disappear, yet it can be summoned again as a bonus action. Your soul weapon cannot be enchanted by spells that enchant weapons.    

Add +2 to your charisma ability score.

Your demonic heritage or your demonic transformation gives you resistance to the damage type that your soul possesses, which is fire, force, lightning, cold, necrotic, or thunder.

Once per short or long rest, a Half-Demon can cast, at will, the False Life spell at 1st level as a bonus action without the need for material, somatic, or verbal components. At 10th and 17th level increase this spells level by one.