Blood magic

Blood magic is a type of evil magic that requires the sacrifice of blood to activate spells, whether it is of the caster or a willing (or sometimes unwilling) participant. Depending on the power of the spell, blood magic can drain a person of their entire life, making it rather deadly.

Empath: The Luckiest Smurf stories
In the EMPATH: The Luckiest Smurf story series, Papa Smurf has learned about blood magic and how dangerous it is, thus he refuses to cast any blood magic spells and has warned his little Smurfs to stay far clear of it. Among humans, it is one of the forbidden magic arts that is never taught in the Sorcerer's Guild.