Eroding Smite

The target takes an extra 2d6 Cold damage from the attack. Inflict 2 stacks of Erosion. Whenever the creature with Erosion takes damage from an attack, deal additional damage based on how many stacks it has. At the start of each of its turns until the spell ends, it may roll a Constitution Saving Throw, on a successful save, remove all Erosion, on failed save, remove 1 Erosion.

Using a Higher-Level Spell Slot. The damage increases by 1d6 and inflicts 1 additional Erosion for each spell slot level above 2.