Many great mortals die without fulfilling their purpose. Archmages, Archdruids, Ancient priests and other powerful people from the past may have been denied or have refused an afterlife. On their quest to accomplish a task they failed in life they roam across the material planes in search of a conduit they trust and attach themselves to a mortal soul. Mortals who are bound to one of these ancient spirits may attempt to fight the spirit or accept it and help the spirit. The Spirit might be so ancient that it's task from beyond the grave might be impossible to achieve. Talk with your DM in what way the spirit is bound to you. Is it in the form of an unremovable necklace or was the spirit bound to you by a ritual.

Soul Bind

When you choose this subclass at 3rd level you are soulbound to an ancient spirit that will assist and guide you in and out of combat. The spirit can move freely within 30 feet of you and can interract with object similarly to the Mage Hand spell with a weight limit of 20 pounds. The spirit can speak to you telepathically and knows common, one language that you know and one extra langauge chosen between; Sylvan, Primordial, Draconic, Infernal, Abyssal, Elven and Undercommon. You learn this extra language as well.
As a bonus action you can make the spirit instantly move to a space within 30 feet of you and attack an enemy that you can see. The spirit's attack uses your Wisdom modifier for attack and damage. The spirit's attack does 1d10+ your Wisdom Modifier of Piercing, Bludgeoning or Slashing damage. The spirit can make a ranged attack with a range of 50/150. The spirit's attacks count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage. The spirit is unaffected by condition effects. The spirit is affected by the Extra attack feature and will attack as many times as you. You can use this ability a number of times equal to half your ranger level and regain all uses of this ability after a long rest.

Twin Soul Magic

Your bound spirit grants you knowledge of their ancient magics.You also learn an additional spell of 1st level or higher when you reach certain levels in this class, as shown in the Twin Soul Spells table. Each spell counts as a ranger spell for you, but it doesn't count against the number of ranger spells you know. At the following levels you learn the following spells:
3rd: Mage armor

5th: Hold person

9th: Phantom Steed

13th: Banishment

17th: Scrying

Spirit Sprint

At 7th level your bond with your spirit enhances your physique, to the rest of the world you are becoming more ghost like.
Your movement speed is increased by 10 feet and you gain 30 feet of climbing speed.
You gain proficiency in Stealth if you do not already, You also have advantage on Stealth checks related so sound.
You gain 60 feet of darkvision if you do not already have it.
Once between short rests when your spirit is away from you, you can use a bonus action to magically switch places with your spirit without provoking attack of opportunity.
Your attacks count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Reincarnation

At 11th level your spirit is powerful enough to bring back a fraction of their ancient power and take over the body of a fallen. 
As an Action you can send your spirit to the non-skeletal corpse of a Medium sized humanoid and take over it. The body takes the appearance of the spirit in life. The Spirit starts using the statblock seen below and acts on your innitiative right after you with full range of actions and reactions.
The spirit's presence in the body causes it to break down rapidly and will last a minute before the body breaksdown beyond use. After a minute the spirit returns to you and can be used as normal. While the spirit is in the body you cannot send him attack or interract but you can still communicate telepathically. You cannot use this action again before the end of a long rest

Keep Me Up

At 15th level your spirit can keep you up even when you are not able to. 
When you hit 0 hitpoints you are not knocked unconcious. Instead your spirit takes over your body and keeps fighting. You must still roll death saves and if you die from failing three death saves or due to damage your spirit cannot keep you up past that point and your body will collapse and die.