You issue a challenge against one creature you can see within range, which must make a successful Wisdom saving throw or become charmed. On a failed save, you can make an ability check as a bonus action. For example, you could make a Strength (Athletics) check to climb a difficult surface or to jump as high as possible; you could make a Dexterity (Acrobatics) check to perform a backflip; or you could make a Charisma (Performance) check to sing a high note or to extemporize a clever rhyme. You can choose to use your spellcasting ability modifier in place of the usual ability modifier for this check, and you add your proficiency bonus if you're proficient in the skill being used. The charmed creature must use its next action (which can be a legendary action) to make the same ability check in a contest against your check. Even if the creature can't perform the action—it may not be close enough to a wall to climb it, or it might not have appendages suitable for strumming a lute—it must still attempt the action to the best of its capability. If you win the contest, the spell (and the contest) continues, with you making a new ability check as a bonus action on your turn. The spell ends when it expires or when the creature wins the contest.