Pact of the Lost

A long time ago you died, maybe from an accident, you had been killed too young. A patron saw you, and saved your soul. They gave you a new body, a recreation of your old one or maybe a new one based on their image. As a Pact of the Lost Warlock you are a ghost, a ghost with a physical form but you are dead. Your soul is connected to your patron, you live because of them and if they get bored they can swiftly throw your soul away. Dying is no longer scaring you've experienced it before. 

Ghostly Projection

Since your soul is only slightly connected to your body, you can easily remove your soul from your physical body as an action. You are able to fly at speed of 40ft. You can move through walls, can talk but only in small whispers, but your vision is only in black and white. You can be seen but have an advantage on stealth in this form. Your body is completely lifeless, if you leave your body for too long it will start decaying. You can pick small objects. When you hit zero hit points you will immediately go into this form. Your max hit points in ghost form is half of your normal hit points. You can cast spells but have disadvantage on all melee attacks,

Possession

After time practicing your abilities you are now able to perform possession. As an action you can poses any creature (with expectations your DM makes). A willing creature may still have slight control but depending on its personality might let you control their body full. An unwilling creature must succeed your spell DC or be fully possessed by you. In this form you take their constitution, strength, and dexterity but keep your own charisma, wisdom, and intelligence, you can cast spells but not any spells this creature might have. You gain abilities of the creature and their health (If they have been damaged that's the health you have until you heal this form). You can attack like normal.

Unbroken Soul

You have advantage on all death saving throws. If you die you get sent to your patron as a soul flickering between life and death. Depending on your relationship with your patron you can be revived instantly. Your physical form is still destroyed if it was damaged in anyway, but your patron can make a new one.

Ghostly Resistance

You are resistant to any non-magical damage. If the weapon is magical and deals physical damage you are not resistant to that attack.