The ghost can travel through objects but if it ends its turn within an object it takes 1d10 force damage. The ghost can only carry clothes, one weapon, armor, and one other non-magical item. A two hour ritual must be performed by the ghost to make these items ethereal. Once ethereal they can also travel through objects with the ghost. Magical items are up to the discretion of the Dm. Weapons that have become ethereal this way are connected to the ghost and deal necrotic damage. 

Choose one ability score to increase by two and another to increase by one

Ghosts live until they solve their unfinished business or are killed

Tieflings are about the same size and build as humans. Your size is Medium.

Your base walking speed is 30 feet. Ghosts can also levitate no more than 5 feet off the ground. 

You have resistance to necrotic damage.

You know the chill touch cantrip. When you reach 3rd level, you can cast the blink spell as a 2nd-level spell once with this trait and regain the ability to do so when you finish a long rest. The ghost can choose what spellcasting ability is the modifier for chill touch. 

You can speak, read, and write whatever languages were spoken in life.