Bartlebee's Symphonic Secrets: Power Chord

You lash out with a powerful blast or musical energy. When you cast this spell you deal 1d8 thunder damage to creature within range. Each friendly creature within 10ft of you may join the power chord. If they succeed on a DC 10 Performance Check.  For each creature who succeeds you may deal an additional instance of damage targeting the same or a different creature. A creature joining the power chord may consume spell slot of equal level to the one you cast. If they do, you may also double the damage of all instances rather than add a new instance.