Blood Ritual

When all else fails, in ancient times there have been rituals known to empower others with temporary strength by sacrificing one self, or another who wishes to sacrifice themselves.

In order to cast this spell, you must have a willing sacrifice, one who is not being forced in any way to sacrifice themselves, (including yourself.) and spend a minute chanting the incantation and drawing the ritual circle around the sacrifice. After the hour is up, you drive the ornate dagger into the body of the sacrifice. The creature is then killed instantaneously. 
(If the sacrifice is a creature that is not a player character, such as a friendly monster that is bound, the dungeon master decides whether or not the sacrifice is willing.) 

The dagger then turns to dust, as the diamond draws all of the power of the creature. The power of the gem is equal to ten times the Challenge Rating (Level if Player Character) of the sacrifice. Any creature to hold this diamond on their person for the next 8 hours, will receive the following benefits;

• Temporary hit points equal to the power in the diamond.
• They may add a 1d6 to any ability check, saving throw, or attack roll they make.
  
  

A creature may only benefit from the effects of this once in their lifetime. Should they attempt to hold or wear a diamond under the effects of this spell ever again the creature then takes 12d12 Necrotic damage. Should the creature continue to hold the diamond, they continue to take the damage at the start of each of their turns.