You brandish the weapon used in the spell's cast-
ing 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 ld8 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 ld8 thunder damage to the target on a hit, and
the damage the target takes for moving increases to
2d8. Both damage rolls increase by ld8 at 1 1th level
(2d8 and 3d8) and again at 17th level (3d8 and 4d8).