Sacrifice Pawn

4th-level necromancy
Casting time: 1 reaction, which you take when a friendly creature within 60 feet drops to 0 hit points
Range: 60 feet
Target: a creature you can see within range
Components: V
Duration: Instantaneous
Classes: Warlock, Wizard
Subclasses:

Sometimes one must fall so others might rise. When a friendly creature you can see within range drops to 0 hit points, you can harness its escaping life energy to heal yourself. You regain hit points equal to the fallen creature’s level (or CR for a creature without a level) + your spellcasting ability modifier.