Clay's Earthen Smite

As you hit the target, a spiritual representation of your weapon strikes the ground beneath the target, rending the ground and turning it into magical difficult terrain. It takes an extra 1d6 Force damage from the attack and must make a Dexterity saving throw or be knocked prone. At the start of each of its turns until the spell ends, the target takes 1d6 Force damage and then makes a Dexterity saving throw. On a failed save, the spell continues. On a successful save, the spell ends and the target may stand up.

Using a Higher-Level Spell Slot. All the damage increases by 1d6 for each spell slot level above 1.