Cursed With Power

Sometimes the threads of magic that run through a sorcerer comes from a cursed source that festers within the soul. Having such a cursed soul is a sign that your innate magic might come from a distant but powerful familial connection to an infernal being. Or perhaps that being is far closer. Perhaps that being is a demon taking refuge from its masters in the souls of each generation of your family. Or your birth might align with an ancient compact, marking you as chattel of a devil or a chosen vessel of fell corruption.
A Cursed Soul, with some infernal habitus, is seen as a threat by some fiendish hierarchies. As an outsider who commands profane power, a Cursed Soul can undermine an existing order by claiming a direct tie to impiety.
Some seek to break the curse, trying to abandon power for humble virtue. Those who do often lose the favour that has shielded them and are soon slain by old enemies. More foolish are those that seek to exert their power in the cause of good. But only ash can come from trusting in the power of fiends.

Cursed Magic

Your link to the fieldish allows you to learn spells from the warlock class. When your Spellcasting feature lets you learn or replace 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 cursed power: rage, change, despair or passion. 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	SPELL
Rage	Hellish Rebuke
Change	Unseen Servant
Despair	Expeditious Retreat
Passion	Charm Person

Change

You learn the Unseen Servant spell, 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.

Despair

You learn the Expeditious Retreat spell, 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.

Passion

You learn the Charm Person spell, 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.

Rage

You learn the Hellish Rebuke spell, 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.

Hint of Degradation

Starting at 1st level, cursed power brings those who oppose you to ruin.  If a hostile creature you can see succeeds on a saving throw or hits with an attack roll, you can roll 2d4 and subtract it from 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.

Empowered Wounding

Starting at 6th level, the cursed energy crawling through you can empower damaging spells.  Whenever you or an ally within 5 feet of you rolls dice to determine the amount of damage a spell inflicts, you can spend 1 sorcery point to reroll any number of those dice once, provided you aren’t incapacitated.  You can use this feature only once per turn.

Ruinous Wings

Starting at 14th level, you can use a bonus action to manifest a pair of spectral wings from your back. When the wings are present, you have a flying speed of 30 feet. The wings last until you’re incapacitated or you dismiss them as a bonus action.
The affinity you chose for your Cursed magic feature determines the appearance of the spectral wings: flaming wings for rage, ragged vulture wings for change, dracolich wings for despair and black feathered dove wings for passion.

Unnatural Fate

At 18th level, even in death you may not die. You gain the ability to come back from lethal injuries. When you are killed, you can choose to hold onto your fate by will alone and resurrect yourself. You reawaken at half your hit points, your creature type changes and you take on an unnatural aspect. Perhaps this was the plan for you all along and you have proven yourself worthy at last.
The affinity you chose for your Cursed Magic feature determines the creature type and unnatural aspect you take on. 

AFFINITY	Creature Type/Unnatural Aspect
Rage	Fiend / reddened skin and flaming crown
Change	Outsider / hollow blackened eye sockets and cracked dry skin
Despair	Undead / oily spit and pale translucent skin
Passion	Aberration / lavender scent and soft tentacled mouth