Wake the Dead

The caster must cut their arm (which does 1d4-1 (1 minimum) slashing damage) and drip blood onto the humanoid corpse's eyes (or sockets), tongue, and nostrils.  If it is missing any of these, the spell will not work. 

The lifeforce returns to the corpse, and while it comes back with full hit points, the corpse is not healed in any way, and the target comes back as sapient undead, not alive.  Any body parts missing remain missing, and any wounds remain open, but not bleeding.  Missing mouth parts (like lips and jaws) and/or lungs will prevent them from speaking properly.  

For the first 10 minutes after they return, the living corpse is dazed and confused, and will only be able to speak and understand Celestial, Infernal, Abyssal, or Sylvan, appropriate to whatever afterlife they just returned from. 

After those first 10 minutes, the living corpse regains all of their original stats, thoughts, memories, and abilities, with the following alterations. 

1. Magical or other types of Healing from any source do nothing to the living corpse. 
2. They are now treated as Undead, rather than their previous species. 
3. They feel no pain and cannot bleed, and therefore have Resistance to slashing, piercing, and bludgeoning damage.
4. As they continue to decay, every day at dawn, their Max HP is permanently reduced by 25%, although this can never go below 1.  
5. They are immune to diseases and poisons and damage caused by the same
6.  They don't need to eat, drink, or breathe, and in fact doing so will cause anything they eat or drink to either remain undigested or flow out through a convenient wound.  
7. They don’t need to sleep, and magic can’t put them to sleep.
8. They can finish a long rest in 4 hours if they spend those hours in an inactive, motionless state, during which they retain consciousness.
9.  Their Charisma is reduced by 10 (to a minimum of 2), and they have Disadvantage on all Persuasion and Performance skill checks.  

Spells like Raise Dead, Resurrection, and Animate Dead will do nothing because they are no longer inanimate corpses, but if they are killed again, those spells then would function normally.  Spells like Control Undead may also affect them normally while they are a living corpse.  

GMs may rule there are other side effects to being a living corpse beyond those listed above.  Paladins, Clerics, Warlocks, and Druids might lose contact with, or have their connection with their otherworldly beings reduced.  Spell casters missing fingers might have Disadvantage casting spells with Somatic components or be unable to cast them at all, and those missing lips or jaws might be unable to cast spells with Verbal components.  Certainly the odor of a rotting corpse will be unpleasant to most.  In some cases, the appearance of the living corpse may be concealed enough that they pass as living if not examined too closely, depending on how decayed their body is.  

Using a Higher-Level Spell Slot. You may Awaken one additional living corpse for each spell slot level above 5.