Arquist's Withering

You cast this spell, point at a creature in range and utter a curse. If the creature fails a Constitution saving throw, it will slowly loose hit points. After every long rest the creature takes, it must make a new Constitution saving throw or loose one hit point from its hit point maximum. When a creature's hit point maximum drops to zero, it dies. Unless dispelled, the curse remains until the creature dies.

A dispel magic, remove curse or greater restoration will remove this curse. Greater restoration will also restore the creature's hit point maximum.