Booming Bullet

You tighten your grip on your firearm imbuing it with a deafening energy. On a hit the next time you use this firearm the target receives the normal damage and effects of the firearm and becomes enshrined in a deafening energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 1d8 thunder damage and gains disadvantage on their next attack against any target other than you. The spell ends if the target makes an attack before your next turn, and if not it ends at the start of your next turn.

This spell’s damage increases when you reach certain levels. At 5th level, the base attack deals an extra 1d8 thunder damage to the target on a hit, and the damage the target takes for moving increases to 2d8. Both damage rolls increase by 1d8 at 11th level (2d8 and 3d8) and again at 17th level (3d8 and 4d8).