Eldritch Soul

Your magic comes from a pact etched into your being. You don't recall making any deals or bargains. Is it a manifestation of your innate magic, or has a higher power granted you it before you were even born?

Level 3: Tainted Soul

By methods unknown, by means alien to the greatest scholars, your innate magic has started a metamorphosis. You manifest a fragment of a warlock pact within your sorcery. 

You learn Eldritch Blast, not counting against your sorcerer cantrips, you gain access to spells on the Warlock spell list and you have the Tomb of Levistus Eldritch Invocation when you reach 5th level.

Level 6: Warped Metamagic

Your sorcery bends like pact magic, unstable, ruthless and under your will.

When you use Metamagic you know on a spell, you may empower it with eldritch influence, spending double the sorcery points to apply one of the following. They can be used twice if you have spare points and use a Metamagic that allows the use of more than one per turn, such as Seeking Spell and Twinned Spell. 

Abyssal Reach: Double the spell’s range. Does not stack with Distant Spell.

Malevolent Gaze: One target has disadvantage on its first saving throw against the spell. Does not stack with Heightened Spell.

Unholy Might: If the spell deals damage, reroll one damage die and take the higher result. Does not stack with Empowered Spell

Additionally, when you cast Eldritch Blast, you may apply Metamagic to it even though it is a cantrip.

Level 14: Evolved Pact

Your patron’s nature bleeds directly into your magic, granting a beneficial effect while also demanding equal exchange.

You can choose to have;

Your hitpoint maximum increase by 1 per level and have 5 feet reduced speed in exchange.

A flight speed equal to your walking speed but cannot swim without it being considered difficult terrain and have disadvantage on ability checks while underwater.

Have truesight outwards of 30 feet but cannot take short rests.

No matter what you choose, you can add your Charisma modifier to Eldritch Blast and its range increases by 1.5x

Aspect of the Owl

You have a flying speed equal to your walking speed, but you cannot swim as easily as others. Moving through water that completely submerges you now costs double movement speed and you have disadvantage on every ability check while completely underwater.

Insurmountable Gaze

You have truesight outwards of 30 feet, but because of that, your mind cannot slow down enough to take short rests.

Robust Constitution

Your hitpoint maximum increases by 1 per sorcerer level but you are 5 feet slower.

Level 18: Apotheosis of the Eldritch

You become a living convergence of pact and blood. Choose a benefit to reap. 

Elder Favour

Somehow, you've gained the attention and respect of an Elder Evil. Whoever, whatever and where it is is unknown to you but the effects are very obvious. Once per week, you can call to the Elder Evil who favored you and request their aid. Depending on what is asked of them, they may demand tribute, worship, a cult of personality or are unwilling. If you are unable or are unwilling to pay them back, the Elder Evil abandons you until you absolve yourself in their eyes.

Eldritch Demigod

Once per long rest, you are able to ascend into a heightened state for a minute, granting two benefits. Your spells ignore resistance to damage, and treat immunity as resistance. During each combat, the first spell you cast does not require a spell slot to be used, but cannot be affected by your Metamagic.

Evolved Sorcery

Whenever you roll damage for spells, you can treat any roll of 1, 2, or 3 as a 4 and once per long rest, you can maximize the damage roll of a number of dice equal to half your Charisma modifier rounded down.

Why Won't You DIE!?

You've become, frankly, incredibly hard, if not impossible to put down for good. You gain proficiency in Constitution saving throws and advantage on death saving throws. Furthermore, your hit point maximum increases by 1 per level.