As part of casting this spell, you must expend a hit die or the spell automatically fails. If you do, choose a creature within range and roll the hit die. The creature loses a number of hit points equal to the result. For the duration of the spell, the creature must make a Constitution saving throw at the end of each of its turns. On a failure, roll the hit die expended to cast this spell again, and the creature loses hit points equal to the result. On a success, this effect ends for the creature