Thundering Blade

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range, otherwise the spell fails. On a hit, the attack does damage as normal, except that the entire attack deals thunder damage instead of its normal type. Additionally, a clap of thunder rings out from your strike, forcing all creatures except yourself and the target within 5 feet of the target to succeed on a Dexterity saving throw or take 1d8 thunder damage.

At 5th level, the melee attack and secondary damage each deal an additional 1d8 thunder damage to their targets. Both damage rolls increase by 1d8 at 11th level (2d8 / 3d8), and 17th level (3d8 / 4d8).