Oblivion Soul

Your unate magic comes from a connection you have with the Plane of Oblivion. A plane of absolute nothingness. Everything obliterates out of existence within it and yet has forms of life, clinging to a dwindling existence. Souls are banished here to be eradicated out of existence. There is no after life for those sent here just oblivion.

Soul Link

Starting at 1st level when you choose this subclass, your soul is tethered to the plane of oblivion; constantly exhausting energy into oblivion to fuel the connection. As  result of this (Despite being alive) your soul no longer exudes life essence. Instead the life essence is constantly collapsing inward causing your soul to appear black and empty. You now appear invisible to undead. Undead of CR 1 and below are unable to see you and respond to your movements as if you were invisible. Additionally any creature that relies on sensing life presence (Ex. a Banshee) to locate you are unable to do so in this manner.

Soul Purge

Starting at 1st level, instead of a normal death save you instead use a Charisma save with a DC 18 - half your sorcerer level rounded down. Additionally if the Oblivion Soul Sorcerer dies his soul is instantly obliterated. (No after life, no resurrection)

Emotionless

Starting at 6th level, you perceive emotions as nothing more than useless feelings, As your soul is connected to oblivion longer and longer, you lose the ability to have emotion. As a result you now gain advantage on all wisdom saving throws. Also once per long rest you can spend 2 sorcerer points to instantly succeed on a wisdom save or wisdom based check. 

Obliterate

Starting at 6th level once per turn, when you cast a spell that does damage you can choose to spend 2 sorcerer points to inflict an extra 2d6 psychic damage. The damage dice is increased to 4d6 at 12th level and to 6d6 at 18th level. If an undead is reduced to 0 hit points or below by this effect, the undead's spirit, essence, soul, or whatever is keeping it animated is obliterated leaving behind an empty husk void of any connection to the negative plane.

Oblivion Mind

Starting at 14th level, when ever you succeed on a wisdom saving throw you are healed for half your sorcerer level (Rounded Down) + the DC for the save.

Soulless

Your soul is completely sunken into  itself and your connection to oblivion has grown exponentially. Starting at 14th level, you become resistant to psychic damage; taking only half of the initial damage (Rounded Down). Additionally any creature that inflicts psychic damage to you will take damage equal to twice the amount inflicted upon you.

Oblivion Soul

Your connection with the Plane of Oblivion has grown to such a degree that you seem to not exist at all. Starting at 18th level, you become immune to the effects of Charm, Fear, and any effect that directly affects your soul. Additionally any undead or celestial creatures are no-longer able to perceive your existence, to these creatures you do not exist and are not present and will not respond to you (Despite being able to see you). Any magic that detects living creatures or magic, are unable to detect your presence. Only undead and celestial creatures of a CR equal to (5 + half your sorcerer level + your Charisma Modifier, rounded down) and above can see and interact with you, but will treat you as if you are not supposed to exist. 

Well of Oblivion

Starting at 18th level (As an Action), you can spend 5 sorcerer points to target a creature with a soul, that you can see, and is within 120 feet of you. The target creature make charisma save of DC = 5 + your spell save. On a fail the target's soul is forced into a portal leading directly to the Plane of Oblivion, leaving behind an empty body. The body (If Not Undead) will remain alive for 24 hours, after which (Unless Kept Alive Somehow: DM's Discretion) the body will die.

The banished soul cannot return by normal means. Once every hour while in the plane, the soul must make a Charisma saving throw of DC 25. If the banished soul succeed 3 saves in a row, their soul manages to escape the plane and will attempt to return to their body. If the banished soul's body is dead or destroyed, the soul will instead be brought to their respective after life to spend the rest of existence or to await resurrection. If the banished soul fails the save 3 times in a row, they become lost forever; eventually ceasing to exist.