Corrupted Soul

Sometimes the spark of magic that fuels a sorcerer comes from a corrupted source that darkens the soul. Having such a tainted soul is a sign that your innate magic might come from a distant but powerful familial connection to a devilish entity. Perhaps your ancestor was an devil, transformed into a mortal and creating powerful spawn to use in some nefarious plan. Or your birth might align with an ancient prophecy, marking you as a vessel of strange magic.

Corrupted Magic

Your link to the 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.

In addition, choose an affinity for the source of your demonic power: evil, law, chaos, or neutrality. You learn an additional spell based on that affinity, as shown below. It is a sorcerer spell for you, but it doesn't count against your number of sorcerer spells known. If you later replace this spell, you must replace it with a spell from the warlock spell list. 

Affinity	Spells
Evil	Hellish Rebuke
Law	Armor of Agathys
Chaos	Charm Person
Neutrality	Protection from Evil and Good

Devils Luck

Starting at 1st level, devilish power guards your destiny. If you fail a saving throw or miss with an attack roll, you can roll 2d4 and add it to the total, possibly changing the outcome.

Once you use this feature, you can’t use it again until you finish a short or long rest.

Killing Spree

Starting at 6th level, the corrupted energy coursing through you fuels your need to kill. Whenever you reduce a creatures health to 0, you regain 1 sorcery point.

Cloak of Hell

Starting at 14th level, you can use your bonus action to drape yourself in a deep shadow that spreads out over a 15 foot radius. This shadow darkens bright light to dim light, or dim light to darkness. Any creatures that rely on sight have disadvantage on attack rolls against you. The shadows last until you're incapacitated, you die, or you dismiss them as a bonus action.

Additionally you can see normally in darkness, both magical and non magical, to a distance of 120 feet.

Devils Advocate

At 18th level, you gain the ability to deal grievous injuries. When you have fewer than half of your hit points remaining, as an action you surround yourself with a magical aura that looks like buzzing flies. The next creature to damage you with a melee attack suffers half your hit point maximum in Poison damage as your insects bore through their flesh, healing you for half the damage. This effect lasts until you have more than half your health, then the aura disappears.

Once you use this feature, you can’t use it again until you finish a long rest.