You've made a mutual pact with a ghost, you'll probably get the point, I'm tired and can't flavor this

Vengeful Spirit

After a long time bonded with the ghost you have become one. Starting at level 15, you have immunity to Bludgeoning, Slashing, and Piercing damage from nonmagical attacks, you can levitate yourself up to 10 feet in any direction and you can pass through walls given there is something on the other side

Your ghost has now gained the ability to materialize into a beast of your choosing. The beast is a phantom and takes no damage, you can communicate telepathically and can see through it's eyes. You also gain immunity to being frightened and charmed.

Friend on the Other Side

Starting at level 3, Whenever you attack an enemy you may choose to mark it until it dies or until you choose to unmark it, a marked creature has disadvantage on a saving throws against you and can be track magically through the plains, you have advantage on attack rolls against the creature and you always know where it is.

 (Also keep in mind that you and the ghost have separate consciouses so your able to talk to the ghost)

People start to feel scared around you so you now have disadvantage on persuasion checks. You also gain advantage in intimidation checks due to your eerie nature

Possession

Starting at level 3, 3 times per long rest you may possess a creature or object as an action 

Possessed objects are able to be moved at will and as if telekinesis were cast on it

Possessed creatures must save on a DC 11 wisdom saving throw or be possessed. Possessed creatures are charmed by you and will do anything you ask if it. Possessed creatures also understand all of your languages and and can communicate telepathicly with you. You can read all of the creatures thoughts and memories while possessed, you may also speak through the creature and see through its eyes. The creature may attack and you control the creature and it's actions in combat. If the creature is issued on a suicidal command it will immediately stop being possessed and will stop being charmed

This ability has a range of 30ft

Ghostly Arsenal

Starting at level 7, whenever you make a ranged attack, you may use your bonus action to travel to the point that the attack lands. You may use this 5 time per short rest

Once every dawn you may travel to the ethereal plane for 6 hours as an action, when there you may return to the material plane with a bonus action

Your location you return to is relative to your location in the ethereal plane and vise versa

 

You have 60ft of darkvision and when in complete darkness you are invisible and have a blindsight of 30ft

Ghostly Embrace

Starting at level 11, you have the inate ability to see possible threats, magic, and you can't be surprised and opportunity attacks don't work on you. Any danger glows a faint red, this includes traps, enemys, and dangerous beasts. Any magic glows a faint blue. Ask your DM secretly if there is any magic or danger. You have advantage and double proficiency on insight checks.

You also have Expertise in stealth checks. You may cast Pass Without Trace, Disguise Self, and Invisibility at will without material components