Mass Power Word Kill (5e Spell)
From D&D Wiki
|Casting time:||1 action|
You call forth raw necrotic energy to compel multiple creatures to die. This spell can affect 1500 hit points of creatures within range.
Starting with the creature that has the lowest current hit points, each creature affected by this spell dies. Subtract each creature's hit points from the total before moving on to the creature with the next lowest hit points. A creature's hit points must be equal to or less than the remaining total for that creature to be affected.