Spectral Infusion

You have been infused with spectral power--your blood contains more ectoplasm than plasma and your bear a striking, ghostly visage that makes you different--much more unique than the other guy. How this occurred is different for each spectral sorcerer: perhaps you were caught in an experimental machine designed to view the realms beyond life; perhaps you were cursed by a powerful lich, or perhaps the magic in your blood had a strange interaction during an attempted possession by a ghost.

No matter the cause, everything has just changed: your new blood grants you the ability to walk through walls, disappear, and fly, and that is only the beginning of your newfound power. But whether you use this spectral energy to be the guardian of life or to impose your will on others, that's up to you.

Ghostly Visage

At 1st level, you can take on a ghostly appearance. As an action on your turn, you gain a spectral aura, and undergo some sort of appearance change, such as snow-white hair or glowing green eyes. Unless someone sees you transform, it takes a Wisdom (Perception) or Wisdom (Insight) check against your spell save DC to recognize you as the same person. While in this form, you gain special properties as you grow in power.

Additionally, whether you are in this form or not, you can sense when an non-corporal undead creature is within 30 feet of you, but not its location.

Vanish

As ghostly power flows through your body, you can temporarily make yourself unseen. At 1st level, you can use your reaction when you are hit by an attack. You become invisible until the start of your next turn, and the triggering attack deals half damage. This invisibility ends early if you attack, cast a spell, or take damage.

Ectoplasmic Body

At 6th level, your body is becoming more attuned to the ghostly powers in your blood, granting you new options for your sorcery points.

For one point, you can become invisible or intangible for 30 seconds. For 2 points, you can gain a fly speed equal to your walking speed for ten minutes. Your invisibility or intangibility ends early if you make an Attack or Cast a Spell with a range other than Self. For 4 points, you can take possession of a humanoid, similar the Ghost's Possession Action, with the save DC for the effect being equal to your Spell Save DC.

Walker in Both Worlds

At 14th level, your very nature has changed. You can count as undead or your normal creature type, depending on which is more advantageous.  Additionally, whenever you cast a spell you can also cast the cantrip Chill Touch as a bonus action, but the target cannot be a creature that was targeted by the first spell. If you had not already learned Chill Touch, you learn it now.

Finally, you are able to absorb a creatures' energy when you defeat it. If you reduce a creature to 0 hit points with Chill Touch, you can regain hit points equal to half the damage dealt.

Mass Possession

Beginning at 18th level, you can channel your ghostly powers to overshadow multiple creatures at once, taking control of their physical forms. You must spend 8 sorcery points to do this, and each creature you target must make a Wisdom Saving Throw against your spell save DC as shadowy images of yourself attempt to enter their bodies. Any creature who fails this save is dominated as in the spell Dominate Person or Dominate Monster. You can overshadow a number of creatures equal to your Constitution modifier plus your Wisdom modifier, minimum 2. You cannot target incorporeal undead, plants, or celestials with this ability.

The mass possession lasts 2d4 rounds, after which you must make a Charisma saving throw equal to 15 + the number of creatures you have overshadowed at the end of each of your turns. If you fail this saving throw, the effect ends and you take 1d10 psychic damage for each creature you overshadowed.

You can end the effect early on your turn without expending an Action.