Infernal Ancestry

From the moment of your birth, you carried with you an aura of evil, a mark of your unholy bloodline. Perhaps this was inflicted unto you by a brutish Orthon somewhere far back in your family's history. Or perhaps your ancestor was a servant of Zariel, or even one of the many cambions who've managed to escape the Nine Hells. Whoever they are, your ancestor's foul blood has made its way to you, and it is oh so eager to be unleashed. But it is yours to unleash, for weal or woe. Burn the world to ash, or wield this power against the forces of evil, the choice is yours.

Dark Magic

Your ancestral link to the Nine Hells allows you to learn spells normally associated with the warlock class. When your Spellcasting feature lets you learn a sorcerer cantrip or a sorcerer spell of 1st level or higher, you can choose the new spell from the warlock spell list or the sorcerer spell list. You must otherwise obey all the restrictions for selecting the spell, and it becomes a sorcerer spell for you. You can speak, read, and write Infernal.

Devilish Sabotage

Starting at 1st level, the influence of the lower planes weakens your enemies. If a creature you can see succeeds on a saving throw against a spell you cast, you can roll 1d10 and subtract it from their roll, possibly changing the outcome. You can use this ability a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Scourge of Baator

Starting at 6th level, you can channel your magic to empower your offensive spells. Once per turn when you roll damage for a sorcerer spell, you can spend 2 sorcery points per spell level (2 for cantrips) to deal maximum damage, instead of rolling. You can use this feature only once per turn.

Hellish Visage

Starting at 14th level, you can use a bonus action to take on a more fiendish form. Your skin becomes red if it isn't already, you grow a pair of horns from your forehead, your fingers extend and their tips become clawed, and you sprout a pair of large bat-like wings from your back. While the wings are present, you have a flying speed equal to your walking speed. These changes last until you're incapacitated, you die, or you dismiss them as a bonus action.

Crimson Surge

Starting at 18th level, you gain the ability to unleash the power of your ancestor as a destructive blast of necrotic magic. As an action, you expend some number of sorcerer points to create an explosion centered on you. Enemy creatures in a 20-foot-radius sphere centered on yourself must make a Dexterity saving throw against your spell save DC. On a failed save, a creature takes damage equal to 1d6 per sorcery point expended or half as much damage on a successful one.

You cannot use this ability again until you finish a long rest.