You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and then becomes sheathed in booming energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 1*D8 thunder damage, and the spell ends.
This spell’s damage increases when you reach certain levels. At 5th level, the melee attack deals an extra 1*D8 thunder damage to the target on a hit, and the damage the target takes for moving increases to 2*D8. Both damage rolls increase by 1*D8 at 11th level (2*D8 and 3*D8) and again at 17th level (3*D8 and 4*D8).