Eldrich Appendage

A glowing appendage made of other worldly energy appears taking the place of either a limb, or lost limb the limb also takes the appearance of its corresponding limb on the other side of the body, that deals 1d4 necrotic damage that then is added to a pool of hit points that can be used to heal yourself or others, functions as lay on hands ability, the pool resets at the end of the duration. the pool doesn't reset if concentration is broken. at 5th level the user can use a bonus action to change the form of the appendage to that of any tool or weapon they have seen. (For example, the appendage can be used as a lockpick or as a hammer when the lockpick fails)

At higher levels

at 5th level damage increases by 1d4 necrotic damage, at 9th level damage increases by 1d4 necrotic damage, at 13th level damage increases by 1d4 necrotic damage, at 17th level damage increases by 1d4 necrotic damage and if it manages to kill a creature of medium or small size it can be revived as a bonus action as an undead version of itself with half its normal hp at a maximum of 20+ warlock level, and a movement speed of 20ft and the creature also gains resistance to necrotic damage and has disadvantage on saving throws.