Discordant Melody

You play a disruptive song aimed at a creature that can hear you within range. The target must succeed on a Constitution saving throw or be stunned for the duration of the spell. While stunned in this way, the target gains vulnerability to thunder damage. If the target was previously immune to thunder damage, it is instead resistant for the duration. If the target was previously resistant to thunder damage, it loses this resistance for the duration. The target can repeat the saving throw at the end of each of its turns to lose the stunned effect however, the resistance changes remain until the spell ends.