Infernal sorcery

Perhaps one of your ancestors was a devil.

Infernal constition

Starting at 1st level, you gain resistance to fire and poison damage. Also, your base AC when you are not wearing armor is 10+you charisma modifier.

Infernal temptation

Starting at 6th level, you gain proficiency with the persuasion skill, then double your proficiency bonus with that skill. Also, you gain the ability to speak infernal.

Wings of death

Starting at 14th level, you sprout infernal wings. You gain a flying speed of 40ft. You also have a +1 bonus to fire damage rolls.

In addition, you can cast the plane shift spell, targeting only yourself. When you cast it this way you must be trying to go to the nine hells, or you must be on the nine hells trying to go to the material plane. You gain the ability do this again when you finish a long rest.

Master of devils

Starting at 18th level, you gain immunity to fire and poison damage. You also gain the benefits of being a fiend, like not taking damage from a warlock's of the fiends hurl though hell ability, but you do not count as a fiend for anything that you do not want to be, such as magic circle or infernal calling. Your charisma score increases by 2, to a maximum of 22.

Also, when you kill a huminiod, you can use your reaction to mentally ask it if it will give you it's soul so that i can keep living. You make a deception check against the creatures insight check. If you win, it becomes a imp under your control. You can have a total of devils under your control equal to your sorcerer level. You can promote your devils to become more powerful. You can promote make a number of your imps equal to your charisma modifier become bearded devils. Each devil follows your verbal commands and returns to you once it's take is done.

Infernal magic

Starting at first level, you learn the command and bane spells. These spell's can't be replaced when you level up. In addition, you can add your charisma modifier to one damage roll on your turn. The damage type must be fire or poison. Once you use this trait you can't use it until you finish a short or long rest, or until you cast the bane or command spell.