You know the thaumaturgy cantrip. When you reach 5th level, you may cast the dispel magic spell as a 3rd-level 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.

Your mixed blood has caused your body to express more of your non human traits in one of two directions

depending on the caste of Devil Dragon being either Winged or Armoured they will undertake a gradual metamorphosis as they age.

Your Strength score increases by 1,your Intelligence score increases by 1,and your Charisma score increases by 1.

Young devil dragons are swift to mature. walking mere hours after hatching, attaining the size and development of a 10-year-old human child by the age of 3, and reach adulthood by 10. They live to be around 100.

Devil Dragons unlike their Dragonborn kin tend towards more neutral alignments due to their hybrid nature overall. Occasional outliers trending towards the evil alignments as they more fully embrace the twin forces of Tiamat and the hells that spawned them while those that oppose them are fewer still but staunch defenders of good.

unlocks at Level 10 a modification to the breath weapon from “Dragonic ancestory” upon use roll 1X d12 die to determine effect

if 1 2 or 3 are rolled the merging of elements is unstable and detonates apon the moment of release the caster must make a CON check to see if the detonated breath weapon escapes the confines of the caster’s mouth if so the caster takes damage of the type the breath weapon consists of

if 4 5 6 7 or 8 are rolled the added negative energy become inert in duering the attempt in which case the “Dragonic ancestory” breath weapon will cast as normal

if 9 10 11 or 12 are rolled the merging is stable and you may add negative energy damage equal to half of the normal damage of the breath weapon 

Devil Dragons are taller and heavier than humans, standing well over 6 feet tall and averaging almost 250 pounds winged while mature armoured Devil Dragons tip scales at nearly 300 at times. Your size is Medium.

Your base walking speed is 30 feet.

You have draconic ancestry. Choose one type of dragon from the Draconic Ancestry table. Your breath weapon and damage resistance are determined by the dragon type, as shown in the table.

Draconic Ancestry

You can use your action to exhale destructive energy. Your draconic ancestry determines the size, shape, and damage type of the exhalation. When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry. The DC for this saving throw equals 8 + your Constitution modifier + your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. After you use your breath weapon, you can’t use it again until you complete a short or long rest.

You have resistance to the damage type associated with your draconic ancestry.

You can speak, read, and write Common, Infernal and Draconic. Draconic is thought to be one of the oldest languages and is often used in the study of magic. The language sounds harsh to most other creatures and includes numerous hard consonants and sibilants.