Bioshock

Make a melee spell attack against a target within range (touch range). On a hit, if the target has 75 hit points or fewer, it dies, and you must succeed on a Constitution saving throw against your own spell save DC or take necrotic damage equal to half of that dealt to the target.  If the target has more than 75 hit points, this spell has no effect.  

This spell has no effect on creatures immune to disease.