The Raven's Hand

Using a bit of material from the Shadowfell, you magically create a shadowy prosthetic arm. This arm can be formed around an existing arm or replace a lost one and functions as a perfect substitute. Until the spell ends you gain the following benefits.

• +2 to AC while not using a shield.
• Immunity to necrotic damage but vulnerability to radiant damage
• Unarmed attacks with this magical prosthetic do 1d6 bludgeoning and 1d8 necrotic damage. A creature hit by this arm must make a Constitution save. On a fail the creature takes an additional 1d8 necrotic damage and the user gains temporary hit points equal to half of all necrotic damage. 

This arm counts as an object and can be directly targeted by an attack. The arm has hit points equal to half of the casters with the same AC as the caster. Direct damage to the arm does not hurt the wielder but left over damage as a result of the arm being destroyed transfers to the caster. Destroying the arm ends the spell.