Legend Killer

You tap into the life force of a creature that is capable of performing legendary actions. When you cast the spell, the target must make a successful Constitution saving throw or lose the ability to take legendary actions for the spell’s duration. A creature can’t use legendary resistance to automatically succeed on the saving throw against this spell. An affected creature can repeat the saving throw at the end of each of its turns, regaining 1 legendary action on a successful save. The target continues repeating the saving throw until the spell ends or it regains all its legendary actions.